octahedral metal clusters as molecular building … · of coordination polymers: synthesis,...

OCTAHEDRAL METAL CLUSTERS AS MOLECULAR BUILDING BLOCKS

OF COORDINATION POLYMERS:

SYNTHESIS, CHARACTERIZATION, AND STUDY OF

THEIR HOST-GUEST INTERACTIONS

BY

LEI CHEN

A Thesis Submitted to the Graduate Faculty of

WAKE FOREST UNIVERSITY GRADUATE SCHOOL OF ARTS AND SCIENCES

in Partial Fulfillment of the Requirements

for the Degree of

MASTER OF SCIENCE

Chemistry

December 2011

Winston-Salem, North Carolina

Approved By:

Abdessadek Lachgar, Ph.D., Advisor

S. Bruce King, Ph.D.

Ronald E. Noftle, Ph.D.

ii

ACKNOWLEDGEMENTS

First, I would like to express my deepest gratitude to my advisor Dr. Abdessadek

Lachgar, for his valuable academic advices, great patience in listening and friendly

communication, and large amount of time he devoted through my research and thesis

writing. I sincerely appreciate his encouragement and motivation to help me to achieve

my career milestone. He was generous to support and seek funding opportunities for my

research, my conference travel, my summer research in Kyoto University, and my

summer internship. Dr. Lachgar is not only a scientific mentor for me, but also a friend, a

role model.

I want to thank past and present members of our research group for their

tremendous help, memorable friendship and huge support. Postdocs (Dr. Jianjun Zhang

and Dr. Changkun Xia); graduate students (Kevin Zhao, Sergio Aaron Gamboa and Ye

Zheng); undergraduate students (Jenny Nesbitt, Noah Grade, and Alex D. MacIntosh).

I would like to thank Dr. Cynthia S. Day in taking great effort to teach me how to

understand crystallography, and provide me hand on experience in operating the single

crystal as well as powder X-ray diffractometers. I want to thank my committee members:

Dr. S. Bruce King and Dr. Ronald E. Noftle for their inspiring suggestions and remarks. I

deeply appreciate that they can understand my situation to send the whole thesis by the

very last minute, and take so much effort and personal time to review my work.

I want to thank Wake Forest University Chemistry Department to provide

generous financial support and enriched research environment for my graduate education.

iii

I also want thank all faculty and staff in the Chemistry Department to provide accessible

help. Also Thanks to all my friends at Wake Forest University to share with me your

happiness and stories, you always stimulate and cheer me up.

Finally, it is beyond my vocabulary to find words to express my appreciation to my

parents and my wife Xueyun Wei for their life care, emotional company, constant

encouragement, and lifetime love.

iv

TABLES OF CONTENTS

CONTENTS························································································iv

ABSTRACT·······················································································xiii

LIST OF FIGURES··············································································viii

LIST OF TABLES················································································ xi

Chapter I: Introduction···········································································1

1. The molecular building block approach to the assembly of coordination polymers·····1

1.1 General synthesis strategies and applications to coordination polymers and

hybrid materials·······················································································2

Chapter II: General methods of synthesis and characterization··························6

1. General methods of synthesis····································································6

2. Methods of Characterization·····································································8

2.1 Structural characterization···································································8

2.2 Phase identification···········································································8

2.3 Elemental analysis············································································9

2.4 Infrared spectroscopy·········································································9

2.5 UV-vis spectroscopy··············································· ··························9

2.6 Cyclic voltammetry (CV) ···································································9

2.7 Magnetic properties measurement························································10

2.8 Thermogravimetric analysis·······························································10

v

Chapter III: Octahedral metal clusters as building blocks·······························12

1. Synthesis and crystal structure of [Ta6Cl12(CN)6]n-

(n=2,3,4) clusters···················13

2. Characterizations of [Ta6Cl12(CN)6]n-

(n=2,3,4) clusters···································16

2.1 Preparation of Na3[Ta6Cl12(CN)6] studied by Uv-vis··································19

2.2 Electrochemical studies····································································20

2.3 Crystal structure of VEC=16 cluster [NMe4]4[Ta6Cl12(CN)6] ························21

2.4 Crystal structure of [Na3(H2O)4(MeCN)2][Ta6Cl12(CN)6] (VEC=15) ···············25

2.5 Crystal structure of the compound [NMe4]2[Ta6Cl12(CN)6] (VEC=14) ·············28

2.6 IR spectroscopy for VEC=14, 15 and 16 metal clusters·······························31

CHAPTER IV: Coordination polymers built of [Ta6Cl12(CN)6]3-

metal clusters and

lanthanides··························································································32

1. Experimental section············································································32

1.1 [La(DMF)(MeOH)1.5(H2O)0.5Ta6Cl12(CN)6]•DMF (1) ································32

1.2 Sm(H2O)2(DMF)Ta6Cl12(CN)6 (2) ·······················································33

2. Crystal structure determinations·······························································33

2.1 Structure of Compound 1··································································33

2.2 Structure of Compound 2··································································38

3. Other physical measurements··································································42

3.1 Thermal stabilities···········································································42

3.2 Infrared spectroscopy·······································································43

vi

CHAPTER V: Positively charged extended frameworks with Ta6 clusters as charge

balancing anions: compounds built of metal clusters, lanthanides and organic

bridging ligands····················································································45

1. Experimental section············································································46

1.1 Synthesis of [Eu(dpdo)(H2O)5(EtOH)2][Ta6Cl12(CN)6]•dpdo•H2O•4MeOH (3) ·· 46

1.2 Synthesis of[Eu(dpdo)3(H2O)4][Ta6Cl12(CN)6]•5H2O (4) ·····························47

1.3 Synthesis of [Eu(dpdo)2(H2O)3Ta6Cl12(CN)6]•2H2O•0.75EtOH (5) ·················47

2. Single crystal X-Ray structure determinations···············································48

2.1 Structure of Compound 3·································································· 48

2.1.1 Structure of compound 3 in the monoclinic form································48

2.1.2 Structure of compound 3 in a triclinic unit cell···································52

2.2 Crystal structure of compound 4··························································55

2.3 Crystal structure of compound 5··························································59

3. Other physical measurements··································································63

3.1 Infrared spectroscopy·······································································63

3.2 Thermogravimetric analysis·······························································65

CHAPTER VI: Coordination polymers formed of [Ta6Cl12(CN)6]3-

and transition

metals or metal complexes·······································································68

1. Frameworks built of metal cluster and zinc dimers·········································68

1.1 [Zn2[Ta6Cl12(CN)6OH] • xH2O (6) ······················································68

1.1.1 Single crystal X-ray structure determinations····································69

vii

2. Porous metal cluster based coordination polymer···········································72

2.1 Zn3[Ta6Cl12(CN)4 X2]2 (X=Cl- or CN

-) (7) ··············································72

2.1.1 Single crystal X-Ray structure determination ····································73

2.1.2 Infrared spectroscopy································································77

2.1.3 Thermogravimetric characterization···············································78

2.1.4 Host guest interaction study·························································79

3. Niobium cyanide cluster with dichlorobis(ethylenediamine)nickel(II) ··················82

3.1 [Ni(en)2]2[Nb6Cl12(CN)6] • 2.5MeOH (8) ···············································82

3.1.1 Single crystal X-Ray structure determinations···································83

3.1.2 Host-guest interaction study························································87

3.1.3 Infrared spectroscopy································································87

3.1.4 Thermogravimetric characterization···············································89

CONCLUSION····················································································90

REFERENCES····················································································91

SCHOLASTIC VITA············································································93

viii

LIST OF FIGURES

Figure 1. Sol–gel chemistry to synthesize hybrid materials····································3

Figure 2. Hydrothermal pathway to synthesize hybrid materials······························4

Figure 3. Direct assembly to synthesize hybrid materials······································5

Figure 4. [(Ta6Li12)X

a6]

n- (L

i = Cl, Br, n = 2, 3, or 4, X

a=outer ligand) ·····················13

Figure 5. Powder X-ray diffraction pattern of LiTa6Cl15 and LiNb6Cl15····················14

Figure 6. Crystal structure of LiNb6Cl15·························································14

Figure 7. Molecular orbital diagram of [M6X18]n-

(M = Nb, Ta, X = Cl, Br, n = 2, 3, 4)·18

Figure 8. UV-vis spectroscopy of the reaction between Ta6Cl14 and NaCN···············19

Figure 9. Cyclic Voltammetry of [Me4N]4[Ta6Cl12(CN)6] in CH3CN·······················21

Figure 10. Crystal structure of [Me4N]4[Ta6Cl12(CN)6] ······································ 22

Figure 11. Powder X-ray Diffraction pattern of [Me4N]4[Ta6Cl12(CN)6] ··················23

Figure 12. Crystal structure of [Na3(H2O)4(MeCN)2][Ta6Cl12(CN)6] ·······················26

Figure 13. Powder X-ray diffraction pattern of [Na3(H2O)4(MeCN)2][Ta6Cl12(CN)6] ···26

Figure 14. Crystal structure of [NMe4]2[Ta6Cl12(CN)6] ······································29

Figure 15. Powder X-ray diffraction pattern of observed [NMe4]2[Ta6Cl12(CN)6] ·······29

Figure 16. (a) The coordination environment of the La3+

ion; (b) The 3D topology

structure; (c) overall 3D structure viewed along a direction··································35

Figure 17. X-ray powder diffraction for compound 1·········································36

Figure 18. (a) The over-all 3D structure viewed along c direction; (b) The coordination

environment of the Sm3+

ion; (c) The coordination polyhedron of the Sm3+

ion··········39


Figure 20. TGA measurement for compound 1·················································43

Figure 21. LaTa7O19 and LaTaO4 confirmation·················································43

ix

Figure 22. Infrared spectroscopy for compound 1·············································44

Figure 23. Infrared spectroscopy for compound 2·············································44

Figure 24. Compound 3 monoclinic structure ··················································49


Figure 26. Compound 3 triclinic structure·······················································53

Figure 27. Compound 4 crystal structure ·······················································56


Figure 29. Compound 5 crystal structure ·······················································60


Figure 31. Infrared Spectroscopy for compound 3, 4, and 5··································65

Figure 32. TGA for compound 3·································································66



Figure 35. Crystal picture for compound 6 under microscope································68

Figure 36. Compound 6 zinc coordination environment······································70

Figure 37. Crystal structure for compound 6 viewing along the c axis······················70

Figure 38. Crystal picture for compound 7 under microscope································73

Figure 39. Crystal structure for compound 7 viewing along the a axis······················74

Figure 40. Pictures of compound 7 as synthesized and upon activation under vacuum···76

Figure 41. Powder diffraction pattern for compound 7········································77

Figure 42. Infrared Spectroscopy for compound 7·············································77

Figure 43. TGA measurement for compound 7·················································78

x

Figure 44. X-ray powder diffraction for the guest diffusion post -synthesis of

compound ···························································································80

Figure 45. Infrared spectroscopy for anisole diffused compound 7··························81

Figure 46. Crystal picture for compound 8 both under normal light and polarizer········83

Figure 47. Crystal structure for compound 8 view along the a axis·························84

Figure 48. Powder diffraction pattern for compound 8········································85

Figure 49. Infrared Spectroscopy for compound 8 and its doping with iodine ············88

Figure 50. Thermogravimetric analysis for compound 8······································89

xi

LIST OF TABLES

Table I. List of Chemicals used in this work·····················································7

Table II. UV-vis spectra for metal cluster compounds········································20

Table III. Crystal data and structure refinement for [Me4N]4[Ta6Cl12(CN)6] ··············24

Table IV. Selected bond lengths (Å) and bond angles (°) for [Me4N]4[Ta6Cl12(CN)6] ···25

Table V. Crystal data and structure refinement for [Na3(H2O)4(MeCN)2][Ta6Cl12(CN)6]27

T a b l e V I . S e l e c t e d b o n d l e n g t h s ( Å ) a n d b o n d a n g l e s ( °) f o r

[Na3(H2O)4(MeCN)2][Ta6Cl12(CN)6] ····························································28

Table VII. Crystal data and structure refinement for [NMe4]2[Ta6Cl12(CN)6] ·············30

Table VIII. Selected bond lengths (Å) and bond angles (°) for [NMe4]2[Ta6Cl12(CN)6] ·31

Table IX. IR peaks interpretation for VEC=14, 15 and 16 tantalum cyanide cluster······31

Table X. Crystal data and structure refinement for

[La(DMF)(MeOH)1.5(H2O)0.5Ta6Cl12(CN)6]•DMF·············································37

Table XI. Selected bond lengths (Å) and bond angles (°) for Compound 1················38

Table XII Crystal data and structure refinement for Sm(H2O)2(DMF)Ta6Cl12(CN)6······41

Table XIII. Selected bond lengths (Å) and bond angles (°) for Compound 2··············42

Table XIV. IR spectroscopy peaks interpretation for compound 1 and compound 2······43

Table XV. Crystal data and structure refinement in the monoclinic form for compound

3·······································································································51

Table XVI. Selected bond lengths (Å) and bond angles (°) for Compound 3 in

monoclinic···························································································52

Table XVII. Crystal data and structure refinement in the triclinic form for compound 3·54

Table XVIII. Selected bond lengths (Å) and bond angles (°) for Compound 3 in

triclinic·······························································································55

xii

Table XIX. Crystal data and structure refinement for compound 4·························58

Table XX. Selected bond lengths (Å) and bond angles (°) for Compound 4···············59

Table XXI. Crystal data and structure refinement for compound 5··························62

Table XXII. Selected bond lengths (Å) and bond angles (°) for Compound 5·············63

Table XXIII. IR spectroscopy peaks interpretation for compound 3, 4 and 5··············64

Table XXIV. Crystal data and structure refinement for compound 6························71

Table XXV. Selected bond lengths (Å) and bond angles (°) for Compound 6·············72

Table XXVI. Crystal data and structure refinement for compound 7························75

Table XXVII. Selected bond lengths (Å) and bond angles (°) for Compound 7···········76

Table XXVIII. IR spectroscopy peaks interpretation for compound 7······················78

Table XXIX. Properties and color change observation using different guest molecules· 79

Table XXX. IR spectroscopy peaks interpretation for compound 7·························81

Table XXXI. Crystal data and structure refinement for compound 8························86

Table XXXII. Selected bond lengths (Å) and bond angles (°) for Compound 8···········87

Table XXXIII. IR spectroscopy peaks interpretation for compound 8 and its doping with

iodine·································································································88

xiii

ABSTRACT

This dissertation work focuses on the use of cyanide-functionalized paramagnetic cluster

[(Ta6Cl12i)(CN)12

a]3-

with valence electron per cluster (VEC) = 15 as molecular building

blocks of coordination polymers. Apical cyanide ligands are used as bridging ligands

between the cluster and other molecular building blocks for the preparation of

supramolecular assemblies with different dimensions. Using the self-assembly approach,

eight new compounds were synthesized and their crystal structures have been determined

from sing crystal X-ray diffraction. Two salts

[La(DMF)(MeOH)1.5(H2O)0.5Ta6Cl12(CN)6]•DMF (1) and Sm(H2O)2(DMF)Ta6Cl12(CN)6

(2) were synthesized using the anion [Ta6Cl12(CN)6]3-

and solutions of La3+

and Sm3+

.

Both 1 and 2 precipitated quickly due to extremely low solubility of the products in the

solvent system used, thus the products lacked crystallinity. The introduction of bridging

ligand 4,4'-dipyridyl N,N'-dioxide (dpdo) enabled the formation of three extended

frameworks [Eu(dpdo)(H2O)5(EtOH)2] [Ta6Cl12(CN)6]•dpdo•H2O• 4MeOH (3),

[Eu(dpdo)3(H2O)4][Ta6Cl12(CN)6] •5H2O (4) and [Eu(dpdo)2(H2O)3 Ta6Cl12(CN)6] •2H2O

•0.75EtOH (5), by using the same starting materials but different stoichiometry and

solvents.

The compound [Zn2[Ta6Cl12(CN)6OH] • xH2O containing the Zn2 dimers was

synthesized and structurally characterized, but it was difficult to prepare the compound

quantitatively for further physical characterization. Two other novel compounds

Zn3[Ta6Cl12(CN)4 X2]2 (7) and [Ni(en)2]2[Nb6Cl12(CN)6] • 2.5MeOH (8) were

synthesized and their host-guest molecular interaction were studied. These results

xiv

illustrate the approach of direct self-assembly is an effective way to prepare metal

clusters based coordination polymers with novel structures and properties.

1

Chapter I: Introduction

1. The molecular building block approach to the assembly of coordination polymers

Hybrid inorganic-organic materials, coordination polymers, and metal organic

frameworks have received considerable attention in recent years. The topology and

function of these materials can, in principle, be controlled through judicious choice of

their molecular components.1 Directed assembly of solids with different dimensions

using carefully chosen molecular building units allows for remarkable control over the

structural and physicochemical properties of materials at the molecular level.2,3

The metal-ligand coordination bond has been widely exploited in organizing molecular

building blocks into diverse supramolecular architectures, making use of the strength of

coordination bonds and directionality associated with metal ions.4-6

When metal ions or

metal complexes and bridging organic ligands are assembled into compounds with one-,

two-, and three-dimensional networks they are referred to as coordination polymers (CPs)

or metal-organic frameworks (MOFs).7-14

In the past two decades, the design and

synthesis of MOFs or CPs by the assembly of metal ions as connecting nodes and organic

ligands as linkers have afforded a great deal of interests among the family of polymers,

inorganic materials, and supramolecular materials. A large number of MOFs exhibiting

high surface area and high porosity retained upon the removal of the solvent molecules

have attracted special interest due to their potential applications in gas storage, ion

exchange, separation, and catalysis.

2

Among the molecular building units being investigated, octahedral metal clusters are

attractive due to their nanometric size, their atom-like behavior, their stability, and

relative ease of functionalization due to the availability of six apical labile ligands, and

electronic flexibility due to the presence of metal-metal bonds.15-22

These octahedral

metal clusters can be rationally functionalized to construct predefined building units that

lead to extended structures with expected topologies and properties.

1.1 General synthesis strategies and applications to coordination polymers

and hybrid materials

Depending on the type and the nature of the organic and inorganic components, specific

chemical pathways can be used to design hybrid materials23

or coordination polymers.

Route A: HERE Conventional sol–gel chemistry.24-27

The use of specific multi-

functional precursors and hydrothermal synthesis is the main methodology. For example,

via conventional sol-gel reactions, amorphous hybrid networks can be obtained through

hydrolysis of organically modified metal alkoxides condensed with simple metal

alkoxides. The framework can trap biocomponents or poly-functional polymers through

H-bonds, π- π interactions, and/or van der Waals interactions. This chemical process is

simple and low cost, and can yield amorphous hybrid materials, which exhibit infinite

microstructures, and can be easily shaped.

3

Figure 1. Sol–gel chemistry to synthesize hybrid materials

(courtesy of Dr. Sanchez23

, used by permission)

Route B: Hydrothermal synthesis. Heating a mixture of organic linkers and inorganic

salts in a solvent give rise to numerous materials, which have extensive applications in

the domain of adsorbents or catalysts. One typical metal framework material MOF 528

was synthesized by this pathway using zinc nitrate and terephthalic acid. These hybrid

materials exhibit high surface areas, like MOF-21029

which has BET surface area 6240

m2g

−1 and hydrogen uptake of about 86 mg of H2 per gram of material at 77 K.

4

Figure 2. Hydrothermal pathway to synthesize hybrid materials

Route C: Direct self-assembly (route C1) and the template dispersion (route C2) of well-

defined nano-building blocks (NBB). These building units can be metal clusters,30

or pre-

or post- functionalized nanoparticles (metallic oxides, metals, chalcogenides, etc).31-34

The use of pre-selected building units has several advantages:

The building components are nanometric, monodispersed, and have better defined

structures, which facilitate the characterization of the final materials

Hybrid materials may have properties that combine those of individual

components

5

Figure 3. Direct assembly for the synthesis of hybrid materials

6

Chapter II: General methods of synthesis and characterization

1. General methods of synthesis

The solid precursor LiTa6Cl15 was prepared by solid-state reactions according to the

published literature.35

Stoichiometric amounts of Ta, TaCl5 and LiCl were loaded into

silica tubes in nitrogen filled glove box. The tubes were then sealed under vacuum by

hydrogen flame and heated at 700 oC overnight. Cyanide functionalized tantalum clusters

[Ta6Cl12(CN)6]n-

(n=2,3,4) were prepared by wet chemistry using Ta6Cl14.8H2O as

precursor and aqueous NaCN, followed by purification and recrystallization (for details

refer to Chapter III). All coordination polymers were prepared by direct reaction of

Na3[Ta6Cl12(CN)6] with other building blocks, and were structurally characterized by

single crystal X-ray diffraction, elemental analysis, and IR. All chemicals were used as

received. Solvents including MeOH, EtOH, MeCN, MeO2, and CH2Cl2, etc., were used

as received. Water was distilled and deionized with a Milli-Q filtering system. Chemical

materials purchased from different chemical companies are listed in Table I.

7

Table I. List of Chemicals used in this work

Chemicals Purity

Alfa Aesar

Ta 99.99%, powder, metal basis

Nb 99.8%, powder, metal basis

LiCl 99%

KCN 96%

[(CH3)4N]Cl4 98%

Fisher Scientific

NaCN technical granular

Sm(NO3)3 99.9%

LaCl3 99.9%

REacton

EuCl3 99.9%

Br2 99%

Sigma Aldrich

TaCl5 99.9%, metal basis

NbCl5 99%, metal basis

4,4'-dipyridyl N,N'-dioxide 98%

NiCl2•4H2O 99%

Bu4NPF6 98%

Acros Organics

Ethylenediamine 99%

8

2. Methods of characterization

2.1 Structural characterization

The crystal structures of new compounds were determined by single crystal X-ray

diffraction (XRD), which allows for accurate identification of molecular structures, and

determination of atomic positions, bond lengths, bond angles, torsion angles, absolute

configurations, and charge densities. Data was collected on a Bruker SMART APEX

CCD diffractometer using Mo-Kα radiation at 193K. Data was corrected for adsorption

effects using the multi-scan techniques (SADABS)36

and the structures were solved and

refined using the Bruker SHELXTL (Version 6.1) Software Package.37

Important details

of data collection and structure refinement are summarized in tables within each chapter.

Selected bond length and angles are also summarized in tables. Generally, during the

refinement of all these structures, thermal parameters for all non-hydrogen atoms were

refined anisotropically while all included hydrogen atoms were generated and refined

isotropically, and exceptions were made when cations and solvents were disordered.

2.2 Phase identification

Powder X-ray diffraction (PXRD) technique is a powerful tool in phase analysis. It is

used to confirm the existence of single phases. Crystalline samples (1~5mg) were

prepared and PXRDs were collected. The observed PXRD was compared to the PXRD

simulated from single crystal XRD analysis to check for purity. For all the powder

patterns in this thesis, data were collected at room temperature using a BRUKER P4

general-purpose four-circle X-ray diffractometer equipped with a GADDS/Hi Star two-

dimensional detector positioned 20 cm from the sample.

9

2.3 Elemental analysis

Elemental analysis of C, N, and H was performed on samples (< 5mg) by Atlantic

Microlab, Inc. GA, USA. The composition comparison between observed and calculated

from the molecular formula determined from single crystal X-ray diffraction was used to

confirm the purity of samples and determine the amount of crystallization solvents.

2.4 Infrared spectroscopy

Infrared spectroscopy was recorded on a PerkinElmer 100 FT-IR attenuated total

reflectance (ATR) spectrometer. IR is used to determine if the cyanide ligand is attached

to the cluster only or if it serves as a bridging ligand between the cluster and other

molecular building blocks. Moreover, the vibration frequency of the CN bond stretch also

depends on the valence electrons per cluster (VEC).

2.5 UV-vis spectroscopy

UV-vis spectroscopy was obtained on a HP 845xUV-vis system. Test sample

(0.1~0.5mL) was dissolved in a 2-3 mL solvent, and transferred to a cuvette to conduct

the data collection. The use of UV-vis spectroscopy can help assign the electronic

absorption bands and determine the charge of the cluster and more specifically the

number of electrons available for metal-metal bonding in the cluster.

2.6 Cyclic voltammetry (CV)

Cyclic voltammetry (CV) was carried out in a three-electrode electrochemical cell (2~3

mL volume capacity) containing a glassy carbon-working electrode, a platinum counter

10

electrode, and a saturated calomel electrode (SCE) as reference electrode at a scan rate of

100 mV/s. Samples concentrations were typically 1.0 mM in MeCN and 0.1 M Bu4NPF6

as the supporting electrolyte. Solutions were purged with argon prior to use and kept

under argon during the experiment. Data was collected using a Pine AFRDE4 (Pine

Instrument Company, Grove City, PA) with bi-potentiostat/waveform generator.

2.7 Magnetic properties measurement

Magnetic susceptibility measurements were performed on a 7 T Quantum Design MPMS

SQUID magnetometer. Measurements of magnetization as a function of temperature

were performed from 1.8 to 300 K in a 5000 G field. Samples were packed as a powder

between cotton plugs, placed into gelatin capsules, cooled in a zero applied field and

measured upon warming. The magnetic data was corrected by using Pascal’s constant

(Bain and Berry) and by using an estimated TIP value (500x10-6 emu/mol, Converse and

McCarley) for the Ta6 complex. Diamagnetic corrections for the gel cap and cotton plugs

were also utilized.

2.8 Thermogravimetric analysis

Thermogravimetric analysis (TGA) measures the weight change in materials as a

function of temperatures. TGA is employed to study the thermal stability of materials and

their possible phase transitions.

In this thesis, samples (10~20 mg) were heated from room temperature to 900-1000 oC

under air or Ar flows using a Perkin Elmer Pyris 1 TGA system. For compound 8,

11

thermogravimetric analysis was performed at 10 K min-1 using a Rigaku Instrument

Thermo plus TG 8120 in a nitrogen atmosphere.

12

Chapter III: Octahedral metal clusters as building blocks

Metal clusters are defined as chemical species, consisting of three or more metal atoms

each of which is connected to at least two other metal atoms by chemical bonds.38

The synthesis, structures, bond-types, physical and chemical properties all make

transition metal clusters a unique class of chemical compounds. Transition metal clusters

are widely employed to study metal-metal bonds running from the single bond to the

collective behavior in the metallic states.

This dissertation work focuses on the use of functionalized octahedral metal clusters as

molecular building blocks of coordination polymers. The metal clusters used consist of

six metal atoms that form a rigid and stable octahedral metal core (M6) (M =

Nb or Ta) supported by 12 edge bridging ligands to form the cluster cation [M6L12]n+

(L =

Cl, Br, n = 2, 3, or 4) which has an atom or ion like behavior. Six additional axial ligands

complete the coordination of each metal atom to form the cluster [(M6L12)X6]n-

(Figure 4).

The six axial ligands are labile, thus the cluster can be functionalized by simple ligand

substitution reactions.39

Octahedral metal clusters can be considered as a nano-size

molecular object of about 1 nm in diameter. When these nano-objects are functionalized

by use of ditopic ligands, that can act as bridging ligands, they can be assembled into

supramolecular 0D assemblies, or infinite 1D, 2D and 3D frameworks. In this work,

octahedral metal clusters were functionalized with cyanide ligands that can serve as

connectors for further assembly.

13

Figure 4. [(Ta6Li12)X

a6]

n- (L

i = Cl, Br, n = 2, 3, or 4, X

a=outer ligand)

1. Synthesis and crystal structure of [Ta6Cl12(CN)6]n-

(n=2,3,4) clusters

The molecular building block was prepared using a step-wise synthesis strategy described

as follows.

i) Synthesis of the precursor LiTa6Cl15: The precursor LiTa6Cl15 was prepared through

solid-state high temperature reactions at 700 oC. An intimate mixture of tantalum

pentachloride (0.14 g, 0.39 mmol), lithium chloride (0.024 g, 0.56 mmol), and excess

tantalum powder (0.33 g, 1.80 mmol) is sealed under vacuum in a quartz tube. The

temperature was gradually heated to 700oC within a 10-hr period and kept at this

temperature overnight.

14

The crystal structure of LiTa6Cl15 is similar to that of LiNb6Cl15. Powder X-ray

diffraction pattern of LiTa6Cl15 was found to be similar to the calculated PXRD of

LiNb6Cl15 from its crystal structures40

and it confirms that LiTa6Cl15 is isostructural with

LiNb6Cl15, as shown in Figure5.

Figure 5. Powder X-ray diffraction pattern of LiTa6Cl15 and LiNb6Cl15

Figure 6 displays the structure of LiTa6Cl15 viewed along the c axis. The compound

features a 3D framework in which each [Ta6Cl18]4-

shares all its six apical chloride

ligands with six neighboring [Ta6Cl18]4-

, with lithium atoms partially occupying the

spheres. Inner chlorine atoms are deleted for clarity.

Figure 6. Crystal structure of LiTa6Cl15

15

ii) Preparation of (Ta6Cl12)Cl2(H2O)4•4H2O: 5g of LiTa6Cl15 was ground in a mortar

and dissolved in 500mL water to give an emerald green aqueous solution. The solution

was filtered to remove any insoluble impurities. To this filtered solution, 500mL of 12 M

HCl was added with stirring, leading to the precipitation of dark green microcrystalline

solid (Ta6Cl12)Cl2(H2O)4•4H2O. The compound was filtered and washed twice with

50mL of HCl and twice with 50mL of diethyl ether to obtain 1.4 g product, yield 28%

based on tantalum.

iii) Synthesis of [Ta6Cl12(CN)6]n-

(n=4,3,2)

1. Preparation of [Me4N]4[Ta6Cl12(CN)6]:

[Me4N]4[Ta6Cl12(CN)6] was prepared by the following reaction: 140mg of

(Ta6Cl12)Cl2(H2O)4•4H2O (0.08 mmol) was dissolved in 20 mL of methanol, then140 mg

of Me4NCl (1.28 mmol) in 20 mL of water was added to this solution, and resulting

solution was stirred at room temperature for 3 hours.

To this solution was added 105.6 mg (1.62 mmol) of KCN in 3mL of water under

nitrogen atmosphere. The resulting green solution was stirred at 80oC for 12 hours. The

solid residue was extracted with hot acetonitrile and 0.11 g (yield 69% based on tantalum)

brown crystalline product can be obtained after rotary evaporation. Crystals are soluble in

water, methanol and DMF.

16

2. Preparation of Na3[Ta6Cl12(CN)6]:

Na3[Ta6Cl12(CN)6] was prepared by the reaction between 150mL methanol solution of

(Ta6Cl12)Cl2(H2O)4•4H2O (1.4g, 0.81 mmol) and 100mL aqueous NaCN (0.79g, 16.27

mmol) under reflux overnight and mild oxidation under air for four days in methanol.

Brown crystalline product can be obtained after rotary evaporation, and extraction using

acetonitrile to give 0.93 g (yield 66% based on tantalum), and it can dissolve in water,

methanol and DMF.

3. Preparation of [Me4N]2[Ta6Cl12(CN)6]:

[Me4N]2[Ta6Cl12(CN)6] was prepared by oxidizing [Me4N]4[Ta6Cl12(CN)6]: 200mg of

[Me4N]4[Ta6Cl12(CN)6] (0.10 mmol) powder was dissolved in 15 mL of CH2Cl2 to give a

blue green solution, and 4 drops of bromine was added to this solution under stirring, and

the resulting solution was left under stirring for 30 minutes to give a red-brown color

solid. Filter to get the solid and wash twice with CH2Cl2 and dry it under vacuum to get

133.1mg red-brown crystalline powder (yield 72% based on tantalum). The solid is not

soluble in water, methanol or DMF.

2. Characterizations of [Ta6Cl12(CN)6]n-

(n=2,3,4) clusters

17

The octahedral metal clusters can have a number of electrons available for metal-metal

bonding referred to as valence electron count (VEC) that ranges from 14 to 16. The VEC

is calculated as follows:

VEC =overall charge of metal d-level electrons+ overall charge of ligands + charge of the cluster

For example, VEC of [(Ta6Cl12)(CN)6]4-

cluster is 16 and is calculated as:

VEC = 6* (+5) +12*(-1)+6*(-1) + 4 = 16

[(Ta6Cl12)X6]n-

can be stabilized in three oxidation states with n=2, 3, and 4, when n=4

the cluster is diamagnetic41

with temperature independent paramagnetism (TIP), thus the

compound containing the [Ta6Cl12]2+

cluster unit has asinglet ground state. Compounds

containing the cluster [(Ta6Cl12)X6]2-

are also diamagnetic. On the other hand, compounds

containing the cluster [(Ta6Cl12)X6]3-

unit are paramagnetic and exhibits magnetic

moments close to the spin-only value of one unpaired electron.41

Molecular orbital calculations for the [Ta6Cl18]4-

show that the 16 valence electrons fill 8

bonding molecular orbitals leaving the remaining 16 anti-bonding orbitals vacant42

. The

most recent DFT (density functional theory) calculations on the electronic structure of

compounds containing octahedral [Ta6 Cli12 X

a6]

4- (X = Cl, Br) show that the nonbonding

a2u level orbital lies between the bonding t2g orbitals and the anti-bonding eu orbitals.43

18

(a) [M6X18]4-

(b) [M6X18]3-

(c) [M6X18]2-

Figure 7. Molecular orbital diagram of [M6X18]n-

(M = Nb, Ta, X = Cl, Br, n = 2, 3, 4)

Electronic spectroscopy for the n = 4 and n = 3 states of the [Ta6Cl12]n+

cores are similar

and this may lead to confusion in assigning the particular electronic transitions of the

clusters, especially in a mixture of clusters in different oxidation states.41,44-46

In both

oxidation states tantalum clusters produce orange-brown to yellow solutions. A more

reduced n = 2 species is easier to identify by a large increase in absorption in the visible

region of the spectroscopy, and the solution is in dark green color.

The goal of my research is to assemble coordination polymers using paramagnetic cluster

[(Ta6Cli12)(CN)

a6]

3- with VEC = 15, and study their magnetic and host-guest interaction

properties.

19

2.1 Preparation of Na3[Ta6Cl12(CN)6] studied by Uv-vis

In the preparation of Na3[Ta6Cl12(CN)6] by reflux reaction of 150mL methanol solution

of (Ta6Cl12)Cl2(H2O)4•4H2O (1.4g, 0.81 mmol) and 100mL aqueous NaCN (0.79g, 16.27

mmol), 0.1 mL aliquots was taken at interval times using auto pipette as the reaction was

going, and was diluted by 2:1 mixture of methanol and water to 2mL, then it was

transferred to a cuvette to take the UV-vis spectroscopy.

(Ta6Cl12)Cl2(H2O)4•4H2O is blue in methanol and shows one absorbance peak at 330nm.

After adding aqueous NaCN, the reaction solution at 20 minutes shows one absorbance

peak at 354nm, and it shifts left after 40, 60, 80 and 100 minutes. The absorbance band is

at 343nm after 240 minutes. The final product of Na3[Ta6Cl12(CN)6] also shows the

absorbance peak at 343nm in the UV-vis spectroscopy. The UV-vis spectrum is shown in

Figure 8.

Figure 8. UV-vis spectroscopy of the reaction between Ta6Cl14 and NaCN

20

[Me4N]4[Ta6Cl12(CN)6] can be dissolved in DMF, and shows the absorbance peak at

343nm. Since the oxidized cluster [Me4N]2[Ta6Cl12(CN)6] cannot be easily dissolved in

common solvents, the UV-vis spectroscopy couldn’t be obtained. The UV-vis spectra for

above mentioned metal cluster compounds are summarized in the Table II.

Table II. UV-vis spectra for metal cluster compounds

Compound Cluster core Solvent Color Peak/nm

(Ta6Cl12)Cl2(H2O)4•4H2O [Ta6Cl12]2+

MeOH Blue 330

[Me4N]4[Ta6Cl12(CN)6] [Ta6Cl12]4+

DMF Cyanine 339

Na3[Ta6Cl12(CN)6] [Ta6Cl12]3+

MeOH Brown 343

2.2 Electrochemical studies

Cyclic voltammetry (CV) was used to study the electrochemical properties of tantalum

hexacyanide cluster. The study can help to determine the oxidizing and reducing agents

that are needed to prepare cluster species with different VECs.

CV of [Me4N]4[Ta6Cl12(CN)6] in CH3CN: 2 mg of [Me4N]4[Ta6Cl12(CN)6] (1mmol)

was dissolved in 1mL acetonitrile to give a cyan colored solution with a concentration of

1mM. 38.7 mg Bu4NPF6 (0.1 mm ol) was added to the above solution while stirring as

electrolyte with a concentration of 0.1M.

21

Two one-electron reduction waves were observed at -0.238 V and 0.348 V vs SCE,

corresponding to [Ta6Cl12(CN)6]4-/3-

and [Ta6Cl12(CN)6]3-/2-

redox couples respectively,

and their corresponding ΔEp values (64 and 55 mV respectively) were corresponding to

one electron redox process. Thus, based on standard electrode potentials in aqueous

solutions at 25 oC, p-benzoquinone/H

+, I2, or O2 should be able to oxidize

[Ta6Cl12(CN)6]4-

into [Ta6Cl12(CN)6]3-

while Br2 or Cl2 could oxidize [Ta6Cl12(CN)6]3-

into [Ta6Cl12(CN)6]2-

.

Figure 9. Cyclic voltammetry of [Me4N]4[Ta6Cl12(CN)6] in CH3CN

2. 3 Crystal structure of VEC=16 cluster [NMe4]4[Ta6Cl12(CN)6]

Dark green plate-like crystals of [Me4N]4[Ta6Cl12(CN)6] suitable for single-crystal X-ray

diffraction were obtained by vapor diffusion of Et2O into its concentrated methanolic

solution..

22

The compound [Me4N]4[Ta6Cl12(CN)6] crystallizes in a C centered monoclinic unit cell,

space group C2/m with two formula units per unit cell. No attempts were made to locate

hydrogen atoms on the half occupied carbon atom, coordinated water and hydroxyl

groups of methanol. The refinement of data gave R1 = 4.86% for observed data and

wR2=9.44% for all data.

Figure 10(a) shows the unit cell of [Me4N]4[Ta6Cl12(CN)6] which contains two clusters

[Ta6Cl12(CN)6]4-

stabilized by 8 [Me4N]+ cations . Figure 10 (b) shows the tetrahedral

environment of the cations [Me4N]+. The average intra-cluster bond lengths are Ta-Ta=

2.8894(5) Å, and Ta-Cl= 2.4693(19) Å. The average Ta-C bond length is 2.258(10)Å and

the Ta-C-N angles range from173.5(12) to178.6(8)o, so the Ta-C-N bond angles are

slightly distorted due to crystal packing and perhaps hydrogen bonding between the

[Me4N]+ and the N end of the CN ligand.

(a) unit cell (b) tetrahedral environment

Figure 10. Crystal structure of [Me4N]4[Ta6Cl12(CN)6]

23

The observed PXRD of [Me4N]4[Ta6Cl12(CN)6] was compared to the calculated PXRD

obtained from its crystal structure as determined for single crystal structural

determination. The two PXRDs are shown in Figure 11 and are matching each other well.

Figure 11. Powder X-ray Diffraction pattern of [Me4N]4[Ta6Cl12(CN)6]

24

Table III. Crystal data and structure refinement for [Me4N]4[Ta6Cl12(CN)6]

Empirical formula C22 H48 Cl12 N10 Ta6

Formula weight (g) 1963.80

Temperature (K) 193(2)

Wavelength (Å) Mo (K)0.71073

Crystal system Monoclinic

Space group C2/m

a (Å) a = 12.3171(16)

b (Å) b = 20.444(3)

c (Å) c = 11.4639(15)

(°) 90

(°) 117.1

(°) 90

Volume (Å3) 2569.6(6)

Z 2

Density (calculated) (g/cm3) 2.538

Absorption coefficient (mm-1

) 13.373

F(000) 1784

Crystal size (mm3) 0.12 x 0.04 x 0.02

Theta range for data collection 3.99 to 27.50°

Index ranges -15<=h<=16, -26<=k<=26,

-14<=l<=14

Reflections collected 11373

Independent reflections 3028 [R(int) = 0.0430]

Completeness to theta = 27.50° 99.5 %

Absorption correction Semi-empirical from equivalents

Max. and min. transmission factor 0.7758 and 0.2968

Refinement method Full-matrix least-squares on F2

Data / restraints / parameters 3028 / 0 / 120

Goodness-of-fit on F2 1.054

Final R indices [I>2sigma(I)] R1 = 0.0387, wR2 = 0.0911

R indices (all data) R1 = 0.0486, wR2 = 0.0944

Largest diff. peak and hole 4.311 and -1.472 e.Å-3

*R= (Fo-Fc) / Fo , **wR = {w [(F2

o F2

c)] / w [(F 2

o ) 2]}

0.5

w = [2(F

2o) + (0.0521P)

2+2.9444P]

1 , where P = (F

2o +2 F

2c)/3

25

Table IV. Selected bond lengths (Å) and bond angles (°) for [Me4N]4[Ta6Cl12(CN)6]

Bond Length (Å) Bond Angle (°)

Ta-C 2.245(11) –2.271(8) C-Ta-Cl 80.2(2) – 81.7(2)

Ta-Cl 2.4688(19) –2.4697(19) Cl-Ta-Cl 88.31(7) – 88.97(10)

Ta- Ta 2.8842(7) – 2.8894(5) Ta-Cl-Ta 71.36(7) –71.67(5)

C≡N 1.119(14) – 1.491(11) Cl-Ta-Cl 161.34(5) – 161.46(7)

Ta-Ta-Ta 59.880(13) –60.062(14)

Ta-Ta-Ta 89.848(15) – 90.152(15)

N≡C-Ta 173.5(12) – 178.6(8)

2.4 Crystal structure of [Na3(H2O)4(MeCN)2][Ta6Cl12(CN)6] (VEC=15)

Brown cubic crystals of [Na3(H2O)4(MeCN)2][Ta6Cl12(CN)6] suitable for single-crystal

X-ray diffraction can be obtained by slow evaporation of its concentrated methanolic

solution.

The compound [Na3(H2O)4(MeCN)2][Ta6Cl12(CN)6] crystallizes in the orthorhombic

system with space group Fddd, with eight formula units per unit cell. The refinement of

data gave R1 = 3.71% for observed data and wR2 =7.74% for all data. Viewing along the

c axis in Figure 12, the clusters [Ta6Cl12(CN)6]3-

are located on the edges of a cube

forming an closed packing. The averaged intra-cluster bond length are Ta-Ta=2.9232(5)Å,

and Ta-Cl= 2.449(2)Å. The average Ta-C distance is 2.223(12) Å and the average Ta-C-

N angle is 180.0(2)o.

26

Figure 12. Crystal structure of [Na3(H2O)4(MeCN)2][Ta6Cl12(CN)6]

Powder X-ray diffraction pattern of observed [Na3(H2O)4(MeCN)2][Ta6Cl12(CN)6]

matched the PXRD calculated from its crystal structure, confirming the purity of the

product.

Figure 13. Powder X-ray diffraction pattern of [Na3(H2O)4(MeCN)2][Ta6Cl12(CN)6]

27

Table V. Crystal data and structure refinement for [Na3(H2O)4(MeCN)2][Ta6Cl12(CN)6]

Empirical formula C6 H4 Cl12 N6 Na3 O2 Ta6



Wavelength (Å) 0.71073

Crystal system Orthorhombic

Space group Fddd

a (Å) a = 19.8418(14)

b (Å) b = 19.8458(14)

c (Å) c = 19.8484(14)

(°) 90

(°) 90

(°) 90

Volume (Å3) 7815.8(10)

Z 8



) 17.599

F(000) 6202



Index ranges -23<=h<=23, -23<=k<=23, -23<=l<=23












*R= (Fo-Fc) / Fo , **wR = {w [(F2

o F2

c)] / w [(F 2

o ) 2]}

0.5

w = [2(F

2o) + (0.031600P)

2+7243.776001P]

1 , where P = (F

2o +2 F

2c)/3

28

Table VI. Selected bond lengths(Å) and bond angles(°) for

[Na3(H2O)4(MeCN)2][Ta6Cl12(CN)6]


Ta-C 2.215(13)~ 2.233(12) C-Ta-Cl 81.70(5)~ 81.72(5)

Ta-Cl 2.446(2)~ 2.450(2) Cl-Ta-Cl 87.93(9)~ 89.69(9)

Ta- Ta 2.9231(5)~ 2.9232(5) Ta-Cl-Ta 73.05(13)~ 73.80(17)

C≡N 1.155(18)~ 1.178(18) Cl-Ta-Cl 163.27(10)~ 163.35(10)

Na-Na 3.34(7) ~ 3.68(8) Ta-Ta-Ta 59.997(9) ~60.001(9)

Ta-Ta-Ta 89.999(18)~ 90.004(18)

N≡C-Ta 180.0 (2)

2.5 Crystal structure of the compound [NMe4]2[Ta6Cl12(CN)6] (VEC=14)

Black cubic crystals of [NMe4]2[Ta6Cl12(CN)6] suitable for single-crystal X-ray

diffraction can be obtained by vapor diffusion of bromine into [Me4N]4[Ta6Cl12(CN)6]

concentrated CH2Cl2 solution.

The compound [NMe4]2[Ta6Cl12(CN)6] crystallizes in a F centered cubic unit cell, space

group is Fd-3m with eight formula units per unit cell. The refinement of data gives R1 =

4.74% for observed data and wR2 =9.78% for all data.

Viewing along the b axis in Figure 14, [Ta6Cl12(CN)6]2-

clusters are located on the corner

of a cubic cell, with one [Ta6Cl12(CN)6]2-

in the center to form the closed packing. The

29

tetramethylammonium groups are not shown for clarity. The average intra-cluster bond

lengths are Ta-Ta= 2.9596(7)Å, and Ta-Cl= 2.434(2)Å. The average Ta-C distance is

2.251(15) Å and the average Ta-C-N angle is 180.000(7)o.

Figure 14. Crystal structure of [NMe4]2[Ta6Cl12(CN)6]

Powder X-ray diffraction pattern of observed [NMe4]2[Ta6Cl12(CN)6] was compared to

the calculated PXRD from single crystal structures, and it confirmed that they have the

same powder diffraction patterns.

Figure15. Powder X-ray diffraction pattern of observed [NMe4]2[Ta6Cl12(CN)6]

30

Table VII. Crystal data and structure refinement for [NMe4]2[Ta6Cl12(CN)6]

Empirical formula C14 H42 Cl12 N8 Ta6




Crystal system Cubic

space group Fd-3m

a (Å) a =20.0127(7)

b (Å) b =20.0127(7)

c (Å) c =20.0127(7)

(°) 90

(°) 90

(°) 90

Volume (Å3) 8015.2(5)

Z 8



) 17.135

F(000) 6592


Theta range for data collection 4.07 to 27.50o

Index ranges -26<=h<=26, -26<=k<=26,

-26<=l<=26


Independent reflections R(int)=0.0459

Completeness to theta = 27.50 99.2 %


Max. and min. transmission 0.6643 and 0.2791


Data / restraints / parameters 387/ 2 / 28





*R= (Fo-Fc) / Fo , **wR = {w [(F2

o F2

c)] / w [(F 2

o ) 2]}

0.5

w = [2(F

2o) + (0.0549P)

2+73.8263P]

1 , where P = (F

2o +2 F

2c)/3

31

Table VIII. Selected bond lengths (Å) and bond angles (°) for [NMe4]2[Ta6Cl12(CN)6]


Ta-C 2.251(15) C-Ta-Cl 82.44(4)

Ta-Cl 2.434(2) Cl-Ta-Cl 88.88(14)~ 89.13(14)

Ta- Ta 2.9596(7) Ta-Cl-Ta 74.87(8)

C≡N 1.05(9)~ 1.504(10) Cl-Ta-Cl 88.88(14)

Ta-Ta-Ta 60

Ta-Ta-Ta 82.44(4)

N≡C-Ta 180.0

2.6 IR spectroscopy for VEC=14, 15 and 16 metal clusters

Observed IR absorption bands for CN and OH stretching vibrations for VEC=14, 15 and

16 tantalum cyanide clusters are shown in Table IX.

Table IX.IR peaks interpretation for VEC=14, 15 and 16 tantalum cyanide cluster

VEC States Chemical Formula Wavenumbers (cm-1

)

16 (Me4N)4[Ta6Cl12(CN)6] νCN=2125, νO-H=1485, νO-H=950

15 Na3[Ta6Cl12(CN)6] νCN=2133

14 (Me4N)2[Ta6Cl12(CN)6] νCN=2227, νCN=2137,

νO-H=1486, νO-H=948

32

CHAPTER IV: Coordination polymers built of [Ta6Cl12(CN)6]3-

metal clusters and

lanthanides

In this study the interaction between paramagnetic octahedral tantalum clusters

[Ta6Cl12(CN)6]3-

and rare earth element was studied. Different rare earth metals lead to

different topology of final coordination polymers.

Two novel compounds were synthesized and their crystal structure analysis were

performed: [La(DMF)(MeOH)1.5(H2O)0.5Ta6Cl12(CN)6]•DMF (1) has (6, 6)-connected 3D

network with a {412

; 63}{4

9; 6

6} topology (topological type: NIA).

47

Sm(H2O)2(DMF)Ta6Cl12(CN)6 (2) has (5, 5)-connected 3D network with a {46; 6

4}

topology (topological type: NOY).47

The compounds were structurally characterized

using single crystal and powder X-ray diffraction, and infrared spectroscopy. Their

thermal stability properties were also investigated.

1. Experimental section

1.1 [La(DMF)(MeOH)1.5(H2O)0.5Ta6Cl12(CN)6]•DMF (1)

To 5.0 mL of 75 mg (0.04 mmol) of [Na3(H2O)4(MeCN)2][Ta6Cl12(CN)6] in methanol

was added 5.0 mL of 75mg aqueous solution of LaCl3 (0.31mmol), and 0.1 mL DMF was

added to the above mixture. Dark brown plate-like crystals formed after 2 days. The

crystals were isolated by filtration, washed with two 5mL portions of cold water and two

5mL portions of MeOH, then dried in air, to yield20 mg crystalline product,

corresponding to 24.8% yield based on [Na3(H2O)4(MeCN)2][Ta6Cl12(CN)6]. Elemental

33

analysis: Calc. for C13.5H21Cl12LaN8O4Ta6: C, 8.07%; H, 1.04%; N, 5.57%; Found: C,

8.04%; H, 1.11%; N, 5.40%. IR: ν(CN) = 2146 cm−1

.

1.2 Sm(H2O)2(DMF)Ta6Cl12(CN)6 (2)

To 5.0 mL of 75 mg (0.04mmol) solution of [Na3(H2O)4(MeCN)2][Ta6Cl12(CN)6] in

methanol was added 5.0 mL of 75 mg aqueous solution of Sm(NO3)3•4H2O (0.17 mmol),

and 0.1 mL DMF was added to above mixture. Dark brown plate-like crystals formed

after 2 days. The crystals were isolated by filtration, washed with two 5mL portions of

water and two 5mL portions of MeOH, and then dried in air to yield 10mg crystalline

product (12.6%) based on [Na3(H2O)4(MeCN)2][Ta6Cl12(CN)6]. Elemental analysis: for

C13.5H21Cl12LaN8O4Ta6: Calc. C, 6.67%; H, 0.83%; N, 5.31%; Found: C, 6.64%; H,

0.86%; N, 5.21%. ν(CN) = 2220 cm−1

).

2. Crystal structure determinations

2.1. Structure of Compound 1

The compound [La(DMF)(MeOH)1.5(H2O)0.5Ta6Cl12(CN)6]•DMF crystallizes in the

monoclinic system, space group P2(1)/c (No. 14), with four formula units per unit cell.

All hydrogen atoms were included in the structural model as fixed atoms on their

respective carbon atoms. The isotropic thermal parameter of hydrogen atom is fixed at a

value 1.2 times the equivalent isotropic thermal parameter of the carbon atom to which it

is covalently bonded. The final anisotropic full-matrix least-squares refinement on F2

with 407 variables converged to R1 = 4.20% for observed data and wR2 = 10.16% for all

data.

34

This compound has a neutral 3D framework containing [Ta6Cl12(CN)6]3-

cluster and La3+

nodes linked to each other by cyanide ligands. Each La3+

ion is coordinated by six

cyanide ligands from six [Ta6Cl12(CN)6]3-

, and three oxygen atoms from three solvent

molecules as shown in Figure 17 (a).

From the connectivity mode point of view, the [Ta6Cl12(CN)6]3-

cluster unit can be treated

as a 6-coordinated octahedral node while the rare earth unit acts as a 6-coordinated node

with trigonal prismatic configuration. The assembly of the two different nodes leads to a

3D framework whose topology can be described as a 6, 6 net with NIA type structure,47

as shown in Figure 16 (b).

The Ta-Ta bond lengths are in the range of 2.9136(7) ~2.9367(8) Å and the average value

is 2.922(6) Å, indicating the presence of paramagnetic [Ta6Cl12(CN)6]3-

clusters with VEC

= 15. The Ta-Cl, Ta-C and C≡N bond lengths and N≡C-Ta bond angles are in the range

2.436(3) ~ 2.462(3) Å (average 2.447(6) Å), 2.232(12) ~ 2.261(14) Å (average

2.24(1) Å), 1.127(17) ~1.165(19) (average 1.14(1) Å) and 172.3(11) ~178.3(15) °

(average 176(2)°). The La-N bond lengths are in the range of 2.612(11) ~2.667(11)Å

while the La-O distances are in the range of 2.516(8) ~ 2.625(11) Å. The ∠C≡N-La

angles are in the range of 161.6(13) ~ 174.7(14)°.

35

(a) (b)

(c)

Figure 16. (a) The coordination environment of the La3+

ion; (b) The 3D topology

structure; (c) overall 3D structure viewed along a direction

The powder X-ray diffraction pattern of observed compound 1 was compared with the

PXRD calculated from its crystal structure. These two PXRDs do not fit well with each

other. The sample is either a different structure or it has impurities. As shown in Figure

17.

36

Figure 17. X-ray powder diffraction for compound 1

37

Table X. Crystal data and structure refinement for

[La(DMF)(MeOH)1.5(H2O)0.5Ta6Cl12(CN)6]•DMF

Empirical formula C13.50 H21 Cl12 La N8 O4 Ta6





space group P2(1)/c

a (Å) a = 10.7507(13)

b (Å) b = 20.683(3)

c (Å) c = 17.955(2)

(°) 90

(°) 90.110(2)

(°) 90

Volume (Å3) 3992.5(8)

Z 4



) 18.254

F(000) 3556


Theta range for data collection 3.90 to 27.50

Index ranges -13<=h<=13, -25<=k<=26,

-23<=l<=23

Reflections collected / unique 36864

R(int) 9110 [R(int) =0.0570]

Completeness to theta = 27.50 99.4 %




Data / restraints / parameters 9110/ 0 / 407





*R= (Fo-Fc) / Fo , **wR = {w [(F2

o F2

c)] / w [(F 2

o ) 2]}

0.5

w = [2(F

2o) + (0.0446P)

2+24.5834P]

1 , where P = (F

2o +2 F

2c)/3

38

Table XI. Selected bond lengths (Å) and bond angles (°) for Compound 1


Ta-C 2.232(12)~ 2.261(14) C-Ta-Cl 79.5(3)~84.3(3)

Ta-Cl 2.436(3)~2.462(3) Cl-Ta-Cl 87.90(11)~89.60(12)

Ta- Ta 2.9136(7)~2.9367(8) Ta-Cl-Ta 73.00(9)~73.69(9)

C≡N 1.127(17)~1.165(19) Cl-Ta-Cl 162.91(12)~163.86(12)

Ta-C 2.232(12)~ 2.261(14) Ta-Ta-Ta 59.579(18) ~60.36(2)

La-N 2.612(11)~2.667(11) Ta-Ta-Ta 89.717(19)~ 90.26(2)

La-O 2.516(8)~ 2.625(11) N≡C-Ta 172.3(11)~178.3(15)

C≡N-La 161.6(13)~174.7(14)

2.2. Structure of Compound 2

The compound Sm(H2O)2(DMF)Ta6Cl12(CN)6 crystallizes in a monoclinic system with

space group P 21/c (No. 14). The monoclinic unit cell contains 4 formula units. No

attempts were made to locate hydrogen atoms on the half occupied carbon atom,

coordinated water and DMF. The refinement of data gives R1 = 5.88% for observed data

and wR2 =10.42% for all data.

This compound has a neutral 3D framework containing [Ta6Cl12(CN)6]3-

and Sm3+

nodes

linked to each other by cyanide ligands. Each Sm3+

ion is coordinated by five cyanide

ligands from five different clusters and three oxygen atoms from three solvent molecules

MeOH, H2O, and DMF as shown in Figure19 (c).

39

From the connectivity point of view, each cluster unit is connected to five Sm3+

and each

Sm3+

is connected to five clusters The assembly of these two different nodes leads to a

3D framework whose topology can be described as a 5, 5 net with the NOY type

structure,48

as shown in Figure 19 (b), and free DMF molecules are captured in the void

of the framework. It is stabilized by hydrogen bond between the carbonyl oxygen atom

and neighboring coordinated solvent molecules.

Ta-Ta bond length is in the range of 2.9126(13) ~ 2.9324(13) Å and the average value is

2.925(6) Å. The Ta-Cl, Ta-C and C≡N bond lengths and N≡C-Ta angle are in the

range of 2.415(7) ~2.469(6)Å, 2.22(2) ~2.29(2)Å, 1.13(3) ~1.19(3)Å and 172.1(19) ~

178(2)°. The Sm-N bond distances are in the range of 2.471(17) ~ 2.540(19)Å while the

Sm-O distances are in the range of 2.371(12) ~ 2.54(2) Å. The ∠C≡N-Sm angles are in

the range of 166(2) ~ 174(2)°.

Figure 18. (a) The over-all 3D structure viewed along c direction; (b) The coordination

environment of the Sm3+

ion; (c) The coordination polyhedron of the Sm3+

ion

(a) (b) (c)

40

The observed PXRD of compound 2 was compared to the calculated PXRD from its

crystal structure. These two diffraction patterns basically match, but the observed powder

pattern doesn’t have high enough resolution to show several specific peaks in the 2θ=5-

10o region.


41

Table XII. Crystal data and structure refinement for Sm(H2O)2(DMF)Ta6Cl12(CN)6

Empirical formula C11 H16.50 Cl12 N7.50 O4 Sm Ta6





Space group P 1 21/c 1 (14)

a (Å) a = 10.7442(12)

b (Å) b = 21.730(3)

c (Å) c = 17.851(2)

(°) 90

(°) 90.0150(10)°

(°) 90

Volume (Å3) 4167.7(8)

Z 4



) 17.866

F(000) 3484


Theta range for data collection 3.90 to 27.50°.

Index ranges -13<=h<=13, -28<=k<=28,

-23<=l<=23












*R= (Fo-Fc) / Fo , **wR = {w [(F2

o F2

c)] / w [(F 2

o ) 2]}

0.5

w = [2(F

2o) + (0.0435P)

2+13.1297P]

1 , where P = (F

2o +2 F

2c)/3

42

Table XIII. Selected bond lengths (Å) and bond angles (°) for Compound 2


Ta-C 2.22(2)~ 2.29(2) C-Ta-Cl 80.6(10)~ 83.8(10)

Ta-Cl 2.415(7)~ 2.469(6) Cl-Ta-Cl 88.61(15)~ 89.3(2)

Ta- Ta 2.9126(13)~ 2.9324(13) Ta-Cl-Ta 73.05(13)~ 73.80(17)

C≡N 1.13(3)~ 1.19(3) Cl-Ta-Cl 163.17(19)~ 164.4(2)

Sm-N 2.471(17)~ 2.540(19) Ta-Ta-Ta 59.708(17) ~60.36(2)

Sm-O 2.371(12)~ 2.54(2) Ta-Ta-Ta 89.87(3)~ 90.18(3)

N≡C-Ta 172.1(19)~ 178(2)

C≡N-Sm 166(2)~ 174(2)

3. Other physical measurements

3.1. Thermal stabilities

Polycrystalline sample of compound 1 is used to study the thermal stability, because it is

easier to prepare in large amount. TGA shows two distinct weight losses in Figure 20.

The first (6.06%) corresponds to loss of all coordinated and free solvent molecules below

200oC (calculated 6.47%). The compound continues to lose weight after 200

oC without

any well-defined phase being formed indicating a continuous decomposition until 800oC

is reached.

43

The final product obtained after 800oC is a mixture of the oxides LaTa7O19 (ICDD

number: 39-0727) and LaTaO4 (ICDD number: 72-1808), as confirmed by PXRD in

Figure 21.

Figure 20. TGA measurement for compound 1 Figure 21. LaTa7O19 and LaTaO4 confirmation

3.2. Infrared spectroscopy

Compound 1 shows νCN =2146 cm−1

, and compound 2 shows νCN = 2220 cm−1

. The

assignments for all the major bands in the spectroscopy are summarized in Table XIV.

Table XIV. IR spectroscopy peaks interpretation for compound 1 and compound 2

Compound Wavenumbers (cm-1

)

1 νCN=2146, νO-H=1492,

νC-O=1378, νO-H=950

2 νO-H=2924, νCN=2220,

νC-O =1380, νO-H=948

44

Figure 22. Infrared spectroscopy for compound 1

Figure 23. Infrared spectroscopy for compound 2

45

CHAPTER V: Positively charged extended frameworks with Ta6 clusters as charge

balancing anions: compounds built of metal clusters, lanthanides and organic

bridging ligands

Even though a number of coordination polymers constructed of octahedral niobium

hexacyanide clusters have been reported,21,22,30,49-53

no coordination polymers based on

analogous tantalum clusters have been reported. Here, we report the first cationic

coordination polymers built of lanthanides and dpdo that encapsulate the paramagnetic

Ta6 cluster with VEC=15. In some of the compounds reported here, the tantalum clusters

do not directly connect with lanthanide, but interact with the cationic framework by weak

hydrogen bonding to the dpdo.

Here we describe the synthesis, structure and properties of three coordination polymers

assembled from the octahedral building blocks [Ta6Cl12(CN)6]3-

, rare earth metal Eu3+

and dpdo ligand. The dimensionality of the frameworks of these compounds can be

controlled by the reaction conditions such as stoichiometry and solvents used.

In the polymer [Eu(dpdo)(H2O)5(EtOH)2][Ta6Cl12(CN)6]•dpdo•H2O•4MeOH (3), Eu3+

ions are connected by neutral dpdo ligands to form cationic layers that are pillared by the

cluster [Ta6Cl12(CN)6]3-

. Structural study of compound 3 indicates that it undergoes an

irreversible crystal to crystal transformation in which the initial monoclinic unit cell is

transformed to a lower symmetry triclinic unit cell after two weeks in the mother solution.

The polymer [Eu(dpdo)3(H2O)4][Ta6Cl12(CN)6]•5H2O (4) consists of Eu3+

connected by

46

dpdo to form cationic 1D zig-zag double-chains with rhombic voids, where the metal

cluster is located. In the compound [Eu(dpdo)2(H2O)3Ta6Cl12(CN)6]•2H2O•0.75EtOH (5),

Eu-dpdo linkages form cationic layers to which a tantalum cluster is directly coordinated

via cyanide ligands.

Compounds 3, 4 and 5 have been characterized by single-crystal and powder X-ray

diffraction, infrared spectroscopy, and thermogravimetric analysis.

1. Experimental section

1.1 Synthesis of [Eu(dpdo)(H2O)5(EtOH)2][Ta6Cl12(CN)6]•dpdo•H2O•4MeOH (3)

Na3[Ta6Cl12(CN)6] 75 mg ( 0.04 mmol) was dissolved in 4 mL MeOH and 1 mL EtOH,

and mixed with EuCl3·6H2O (22 mg, 0.06 mmol) in H2O (14 mL), dpdo (22 mg, 0.1

mmol) in 2 mL MeOH, and 2 mL H2O is then added to the above mixture. The solution is

filtered to remove insoluble materials. The brown solution is transferred to a 20 mL

scintillation vial. Brown needle-like crystals suitable for single crystal X-ray diffraction

formed after one day. The crystals were filtered and washed with two 5 mL portions of

ethanol and allowed to dry in air to obtain 66mg, yielding 70% based on tantalum.

Elemental analysis: Calc. for C34H56N10O16Ta6Cl12Eu: C, 16.16%; H, 2.21%; N, 5.54%.

Found: C, 16.35%; H, 1.89%; N, 5.77%. IR: one characteristic symmetric vibrations

resulting from tantalum cluster νCN=2129 cm-1

,; four characteristic vibrations resulting

from dpdo molecules, νN-O= 1213 cm-1

, νring =1472 cm-1

, νC-H=1181 cm-1

, and νN-O =837

cm-1

.

47

1.2 Synthesis of[Eu(dpdo)3(H2O)4][Ta6Cl12(CN)6]•5H2O (4)

Na3[Ta6Cl12(CN)6] 75 mg (0.04 mmol) was dissolved in 5 mL EtOH, and mixed with a

solution of EuCl3·6H2O (22 mg 0.06 mmol) in H2O (5 mL). Crystalline dpdo (22 mg, 0.1

mmol) was added to the above mixture. The brown solution mixture was stirred for 5

minutes and filtered to remove any remaining solids, then transferred to a 20 mL

scintillation vial. Brown plate-like crystals formed after one week to obtain 55 mg of (4),

yielding 51% based on tantalum. Elemental analysis: Calc. for C36H42N12O15Ta6Cl12Eu:

C, 16.98%; H, 1.66%; N, 6.60%. Found: C, 16.84%; H, 1.60%; N, 6.62%. IR: two

characteristic symmetric vibrations resulting from tantalum cluster νCN=2134 cm-1

, νCN=

2084 cm-1

four characteristic vibrations from dpdo molecules, νN-O = 1220 cm-1

, νring

=1469 cm-1

, νC-H=1180 cm-1

, and νN-O =835 cm-1

.

1.3 Synthesis of [Eu(dpdo)2(H2O)3Ta6Cl12(CN)6]•2H2O•0.75EtOH (5)

Na3[Ta6Cl12(CN)6] (75 mg, 0.04 mmol) was dissolved in 5mL EtOH, and mixed with a

solution of EuCl3·6H2O (22 mg 0.06 mmol) in H2O (2 mL). Solid dpdo (22 mg, 0.1 mmol)

was added to the above mixture. The brown solution was stirred for 5 minutes, filtered,

and transferred to a 20 mL scintillation vial. Dark brown block-like crystals formed after

one week to obtain 49 mg of (5), yielding 50% based on tantalum. Elemental analysis:

Calc. for C27.5H30.5N10O11.75Ta6Cl12Eu: C, 14.24%; H, 1.31%; N, 6.03%. Found: C,

14.29%; H, 1.36%; N, 6.00%. IR: two vibrations resulting from tantalum cluster

νCN=2139 cm-1

, νCN= 2129 cm-1

,; four characteristic vibrations resulting from dpdo

molecules, νN-O = 1229 cm-1

, νring =1479 cm-1

, νC-H=1180 cm-1

, and νN-O =842 cm-1

.

48

2. Single crystal X-Ray structure determinations

Compounds 3-5 were obtained from methanol or ethanol solution by a “one-pot” reaction

of EuCl3·6H2O with bridging ligand dpdo in the presence of the hexacyanide metal

cluster, [Ta6Cl12(CN)6]3-

. Compounds 3-5 have different compositions and structures,

although similar reaction conditions were employed for the three compounds.

Crystals of 3 and 5 are stable in air and don’t change color upon exposure to moisture, or

after solvent removal under vacuum at room temperature. On the other hand crystals of 4

are stable in air but change color from brown to green after vacuum activation at room

temperature.

2.1 Structure of Compound 3

2.1.1 Structure of compound 3 in the monoclinic form

Compound 3 crystallizes in a C centered monoclinic unit cell, with space group C2/m,

with two formula units per unit cell. The position of the hydrogen atoms of the ligands

were calculated and refined using a riding model. Hydrogen atoms of the coordinated

water molecules were located from the electron density map, and refined by fixing the O-

H bond at 0.85 Å. The refinement of data resulted in R1 = 5.25% for observed data and

wR2 =11.40% for all data. Crystal parameters, data collection, and refinement results for

compound 3 are shown in Table XV and Table XVI.

Each Eu3+

ion is connected with two dpdo ligand by the oxygen ends of dpdo to form two

edges of the rhombic void. Layered Eu-dpdo chains form the rhombic void to

accommodate the metal cluster. As shown in Figure 24. Water and methanol molecule

49

are located in the void of the framework, and oxygen atoms in coordinated solvents can

stabilize [Ta6Cl12(CN)6]3-

cluster by hydrogen bond. The Eu3+

atoms are surrounded by

many oxygen atoms from the solvent, making complete crystal structure refinement

difficult.

The Ta-Ta bond length is in the range of 2.9074(10)~2.9233(9) Å and the average value

is 2.9191(6) Å. Ta-Cl= 2.437(3) ~2.441(3) Å, Ta-C=2.226(17) ~2.234(11)Å, the average

Ta-C-N angle is 176.4(18)o. Eu

3+ ions are connected by oxygen atom in c axis direction,

∠Eu-O-Eu angle is 180.0° lined in the c axis direction. The closest distance between

nitrogen atoms in the cyanide ligand with solvent oxygen atoms are 3.340Å and 3.851Å.

a) Eu3+

coordination environment b) Compound 3 view along c axis

Figure 24. Compound 3 monoclinic structure

PXRD of compound 3 was compared to the PXRD calculated from its crystal structure.

Compound 3 is not pure or is a mixture of monoclinic and triclinic phases.

50


51

Table XV. Crystal data and structure refinement in the monoclinic form for compound 3

Empirical formula C26 H16 Cl12 Eu N10 O8 Ta6





Space group C2/m

a (Å) a = 18.362(6)

b (Å) b = 18.200(6)

c (Å) c = 8.694(3)

(°) 90

(°) 107.364(5)

(°) 90

Volume (Å3) 2773.0(15)

Z 2



) 13.523

F(000) 2022



Index ranges -21<=h<=21, -21<=k<=21,

-10<=l<=10


Independent reflections 0.0577 [R(int) = 0.0577]










*R= (Fo-Fc) / Fo , **wR = {w [(F2

o F2

c)] / w [(F 2

o ) 2]}10

0.5

w = [2(F

2o) + (0.0605 P)

2+42.51P]

1 , where P = (F

2o +2 F

2c)/3

52

Table XVI. Selected bond lengths (Å) and bond angles (°) for Compound 3 in monoclinic


Ta-C 2.226(17) ~2.234(11) C-Ta-Cl 81.3(3)~ 82.7(5)

Ta-Cl 2.437(3) ~2.441(3) Cl-Ta-Cl 87.90(12)~ 89.48(12)

Ta- Ta 2.9074(10)~2.9233(9) Ta-Cl-Ta 73.25(7)~ 73.54(9)

C≡N 1.15(2)~ 1.349(18) Cl-Ta-Cl 163.47(8)~ 163.55(10)

Eu-O 2.10(3)~ 2.49(3) Ta-Ta-Ta 59.887(16) ~60.21(2)

Eu-Eu 3.330(8) Ta-Ta-Ta 89.87(3)~ 90.0 (2)

N≡C-Ta 176.4(18)~ 176.4(18)

Eu-O-Eu 180.0

2.1.2 Structure of compound 3 in a triclinic unit cell

Crystals of compound 3 convert from monoclinic symmetry to triclinic symmetry after

about two weeks in the mother solution, the overall framework did not change but

various oxygen atoms and their occupancies were adjusted. The space group is P-1 with

one formula unit per unit cell. The refinement method is the same as compound 3 refined

in the monoclinic system. The refinement of data gives R1 = 6.52% for observed data and

wR2 =12.91% for all data.

Each Eu3+

ion is connected with two dpdo ligands by the oxygen ends to form two edges

of the rhombic void. Two Eu3+

ions are connected by oxygen atoms with ∠Eu-O-Eu

angle 180.0°. Compared with the monoclinic structure to give a clear view of framework

53

in the c axis, the triclinic structure will give a similar structure topology along a axis.

Water and methanol molecules are located in the void of the framework, and the oxygen

atom in coordinated solvents stabilizes [Ta6Cl12(CN)6]3-

cluster by hydrogen bond. The

closest distance between the nitrogen on the cyanide ligand with two closest oxygen

atoms are 3.271Å and 3.545Å. The structure is shown in Figure 26.

The Ta-Ta bond length is in the range of 2.9066(14) ~ 2.9243(13)Å and the average

value is 2.9181(6)Å. Ta-Cl=2.434(5) ~ 2.458(8)Å, Ta-C=2.237(14) ~ 2.24(3)Å, the

average Ta-C-N angle is 173.3(3) o.

a)Eu3+

coordination environment b) Compound 3 view along a axis

Figure 26. Compound 3 triclinic structure

54

Table XVII. Crystal data and structure refinement in the triclinic form for compound 3





Crystal system Triclinic

Space group P-1

a (Å) a = 8.694(3)

b (Å) b = 12.922(4)

c (Å) c = 12.931(4)

(°) 89.493(4)

(°) 77.809(3)

(°) 77.716(3)

Volume (Å3) 1386.5(7)

Z 1

Diffractometer Bruker Smart CCD



) 13.519

F(000) 995



Index ranges -10<=h<=10, -15<=k<=15,

-15<=l<=15












*R= (Fo-Fc) / Fo , **wR = {w [(F2

o F2

c)] / w [(F 2

o ) 2]}10

0.5

w = [2(F

2o) + (0.0712 P)

2+9.48 P]

1 , where P = (F

2o +2 F

2c)/3

55

Table XVIII. Selected bond lengths (Å) and bond angles (°) for Compound 3 in triclinic


Ta-C 2.237(14) ~2.24(3) C-Ta-Cl 81.5(8)~ 81.5(8)

Ta-Cl 2.434(5) ~2.458(8) Cl-Ta-Cl 88.6(2)~ 89.0(3)

Ta- Ta 2.9066(14)~ 2.9243(13) Ta-Cl-Ta 73.18(15)~ 73.58(9)

C≡N 1.21(5)~ 1.37(5) Cl-Ta-Cl 163.5(3)~ 163.6(2)

Eu-O 1.97(6)~ 2.699(3) Ta-Ta-Ta 59.90(4) ~60.26(3)

Eu-Eu 3.332(6) Ta-Ta-Ta 90.06(5)~ 90.16(3)

N≡C-Ta 175(2)~ 178(5)

Eu-O-Eu 180.0

90(2) ~98(3)

2.2 Crystal structure of compound 4

The structure was solved in the space group P2/n, with Z = 2. The structural model

incorporated anisotropic thermal parameters for all non-hydrogen atoms and isotropic

thermal parameters for all hydrogen atoms. No attempts were made to locate hydrogen

atoms on the coordinated water and hydroxyl groups of methanol. The refinement of data

gave R1 = 2.85% for observed data and wR2 =6.08% for all data.

Four dpdo molecules connect with one europium to form two zig-zag chains that stack to

for layers. [Ta6Cl12(CN)6]3-

clusters are located between the chain layers. The layers are

held together by electrostatic interactions with the cluster trianion [Ta6Cl12(CN)6]3-

,

56

hydrogen bonding between oxygen atoms from Eu, and π- π stacking of dpdo. The

shortest distance between nitrogen end of the cyanide ligand and the oxygen atoms on the

Eu3+

is 2.850Å as shown in Figure 27,

The Ta-Ta bond length is in the range of 2.9134(4)~ 2.9356(3)Å and the average value is

2.9271 (7)Å. Ta-Cl=2.4333(11) ~2.4675(13)Å, Ta-C=2.235(5) ~2.255(5)Å, the average

Ta-C-N angle is 174.03(4)o.

(a) Europium-dpdo chain (b) Metal cluster in the chain

Figure 27. Compound 4 crystal structure

The purity of compound 4 was confirmed by comparing the observed PXRD of

compound 4 with the PXRD calculated based on the crystal structure determined from

single crystal x-ray diffraction analysis as shown in Figure 28.

57


58

Table XIX. Crystal data and structure refinement for compound 4






Space group P2/n

a (Å) 15.5964(11)

b (Å) 10.7911(8)

c (Å) 17.6289(13)

(°) 90

(°) 96.267(1)

(°) 90

Volume (Å3) 2949.3(4)

Z 2



) 12.742

F(000) 2334



Index ranges -20<=h<=20, -14<=k<=13,

-22<=l<=22






Refinement method Semi-empirical from equivalents

Data / restraints / parameters 6238/ 8 /403





*R= (Fo-Fc) / Fo , **wR = {w [(F2

o F2

c)] / w [(F 2

o ) 2]}

0.5

w = [2(F

2o) + (0.0282P)

2+5.5968P]

1 , where P = (F

2o +2 F

2c)/3

59

Table XX. Selected bond lengths (Å) and bond angles (°) for Compound 4


Ta-C 2.235(5) ~2.255(5) C-Ta-Cl 80.51(13)~ 84.13(13)

Ta-Cl 2.4333(11) ~2.4675(13) Cl-Ta-Cl 87.97(4)~ 90.24(4)

Ta- Ta 2.9134(4)~ 2.9356(3) Ta-Cl-Ta 72.96(4)~ 73.89(3)

C≡N 1.129(6)~ 1.147(7) Cl-Ta-Cl 163.24(4)~ 163.83(4)

Eu-O 2.375(3) ~ 2.375(3) Ta-Ta-Ta 59.774(6) ~60.236(8)

Ta-Ta-Ta 89.853(5)~ 90.145(5)

N≡C-Ta 173.0(5)~ 176.1(4)

Eu-O-Eu 114.2(2)~146.17(13)

77.04(13) ~79.30(13)

2.3. Crystal structure of Compound 5

The crystal structure of compound 5 was solved in the space group P2(1)/c, with Z = 4.

The structural model incorporated anisotropic thermal parameters for all non-hydrogen

atoms except the half occupied carbon atom and isotropic thermal parameters for all

hydrogen atoms. The refinement of data gives R1 = 3.16% for observed data and wR2

=6.55% for all data.

One europium connect with four dpdo ligands and one cyanide ligand from the cluster, as

displayed in Figure 29 (a), to form the 3D framework. Two dpdo ligands coordinate to

one Eu3+

on the top of the square planar, and two dpdo ligands are connecting with this

60

Eu3+

at the bottom of the square planar. One cyanide ligand is connecting with one Eu3+

.

The cluster is located in the cage viewing along c axis as shown in Figure 29 (b).

The Ta-Ta bond length is in the range of 2.9194(3) ~ 2.9437(3)Å, and the average value

is 2.9294 (3)Å. Ta-Cl=2.4371(12) ~ 2.4608(13)Å, Ta-C=2.242(5) ~ 2.276(6)Å, the

average Ta-C-N angle is 174.05(5)o.

Tantalum clusters are also stabilized by hydrogen bonding between oxygen atoms from

solvent molecules, and π- π stacking of dpdo. The distance between nitrogen on the

cyanide ligand with two closest oxygen atoms are 3.079Å and 4.872 Å.

(a) coordination environment of Eu3+ (b) Structure of one layer:

Figure 29. Compound 5 crystal structure

PXRD of compound 5 is compared to the calculated PXRD from its crystal structures,

and the observed pattern is more broad in the 2θ=5-15o region, but basically they have

very similar powder diffraction patterns.

61


62

Table XXI. Crystal data and structure refinement for compound 5

Empirical formula C27.50H30.50Cl12EuN10O9.75Ta6





Space group P2(1)/c

a (Å) a = 17.5218(10)

b (Å) b = 18.0708(10)

c (Å) c = 16.4071(9)

(°) 90

(°) 93.5480(10)

(°) 90

Volume (Å3) 5185.1(5)

Z 4



) 14.471

F(000) 4194



Index ranges -22<=h<=22, -23<=k<=23,

-20<=l<=20







Data / restraints / parameters 10829/ 0 /588





*R= (Fo-Fc) / Fo , **wR = {w [(F2

o F2

c)] / w [(F 2

o ) 2]}

0.5

w = [2(F

2o) + (0.0250P)

2+24.9567P]

1 , where P = (F

2o +2 F

2c)/3

63

Table XXII. Selected bond lengths (Å) and bond angles (°) for Compound 5


Ta-C 2.242(5) ~2.276(6) C-Ta-Cl 78.47(14)~ 84.36(14)

Ta-Cl 2.4371(12)~ 2.4608(13) Cl-Ta-Cl 87.35(5)~ 90.77(5)

Ta- Ta 2.9194(3)~ 2.9437(3) Ta-Cl-Ta 73.28(3)~ 74.23(3)

C≡N 1.142(8)~ 1.156(8) Cl-Ta-Cl 162.90(5)~ 163.96(4)

Eu-N 2.569(5) Ta-Ta-Ta 59.603(8) ~59.603(8)

Eu-O 2.342(4) ~2.391(4) Ta-Ta-Ta 89.520(9)~ 90.116(8)

N≡C-Ta 168.5(5)~ 177.6(5)

O-Eu-O 79.88(15) ~ 96.29(16)

144.54(14) ~150.15(14)

3. Other Physical Measurement

3.1 Infrared spectroscopy

It can be observed that for the free dpdo ligand, νN-O is 1241 cm-1

, but when it is

incorporated into the frameworks of compound 3, it is shifted to 1213 cm-1

. When dpdo is

in compound 4, νN-O is 1220 cm-1

; when it is in compound 5, νN-O is 1229 cm-1

. νN-O shifts

in these compounds are the result of coordination between dpdo and Eu3+

.

Two absorption bands are observed for CN stretching vibrations in compound 4, 2134

cm-1

and 2084 cm-1

, which are assigned to the two different types of cyanide, one is

64

bonded to Eu3+

ion and the other one is stabilized by the hydrogen bonding with dpdo

ligand.

For compound 5 two CN stretching absorption bands are observed at 2139 cm-1

and 2129

cm-1

, which are assigned to two different types of cyanide, one is directly bonded to Eu3+

ion and the other is connected to the cluster only. The IR spectroscopy is shown in Figure

31. The assignments for all the major bands in the spectroscopy are summarized in the

Table XXIII.

Table XXIII. IR spectroscopy peaks interpretation for compound 3, 4 and 5


)

3 νCN=2129, νring =1472

νN-O= 1213, νN-O =837

4 νCN=2134, νring =1469

νN-O = 1220, νN-O =835

5 νCN=2139, νring =1479

νN-O = 1229, νN-O =842

65

Figure 31. Infrared Spectroscopy for compound 3, 4, and 5

3.2 Thermogravimetric analysis

Thermogravimetric analysis of compound 3 in air shows a weight loss of 7.0 % in the

temperature range of 20–200oC, corresponding to loss of one water and four methanol

molecules (Calculation 6.5%). The weight loss 28% in the temperature range of 200–800

oC corresponds to the loss of dpdo ligands and cyanide ligand and the disruption of the

structural skeleton, as shown in Figure 32. The total weight loss is 35%.

66

Figure 32. TGA for compound 3

Thermogravimetric analysis of compound 4 in O2 shows a weight loss of 7.5 % in the

temperature range of 20–200oC, corresponding to nine water molecules (Calculation

6.4%). The weight loss 26.5% in the temperature range of 200–600 oC corresponds to the

loss of dpdo ligands and cyanide ligand and the disruption of the structural skeleton. The

total weight loss is 34%. As is shown in Figure 33.


67

Thermogravimetric analysis of compound 5 in O2 shows a weight loss of 5.2 % in the

temperature range of 20–200oC, corresponding to nine water molecules (Calculation

5.3%). The weight loss 16.1% in the temperature range of 200–600 oC corresponds to the

loss of dpdo ligands and cyanide ligand and the disruption of the structural skeleton. The

total weight loss is 35%. As is shown in Figure 34.


The thermogravimetric analysis for compound 3, 4 and 5 suggest that three types of

frameworks have similar thermal stabilities. Especially they all have a sharp lost at 500oC,

which indicates the framework would be thermally stable.

68

CHAPTER VI: Coordination polymers formed of [Ta6Cl12(CN)6]3-

and transition

metals or metal complexes

1. Frameworks built of metal cluster and zinc dimers

1.1 [Zn2(OH)[Ta6Cl12(CN)6] • xH2O (6)

Layering 1 mL 2 mM of Na3Ta6Cl12(CN)6 in MeOH on top of 1 mL 3 mM zinc acetate

aqueous solution in a 6 mm diameter glass tube. Brown needle-like single crystals are

observed at the interface between the two solutions after ten days. Picture for the crystal

under optical microscope is shown in Figure 35.

Figure 35. Crystal picture for compound 6 under microscope

Much effort has been spent to prepare the material quantitatively but without success.

Large scale preparations attempts all led to formation of a new compound that

corresponds to the formula Zn3[Ta6Cl12(CN)4 X2]2 (7) (vide infra). For instance, by

stirring 10mL 2mM of Na3Ta6Cl12(CN)6 in MeOH with 10 mL 3mM aqueous solution of

zinc acetate, crystalline materials precipitates and PXRD showed that it corresponds to

compound 7, by comparing observed powder pattern with calculated pattern from

compound 7 single crystal XRD study.

69

1.1.1 Single crystal X-ray structure determinations

Single crystal of compound 6 suitable for single-crystal X-ray diffraction can be obtained

by using 1 mL pipette to take crystals from the methanol/water boundary. Compound 6

crystallizes in a C centered monoclinic system C2/c, with eight formula units per unit cell.

The refinement of data resulted in R1 =6.26% for observed data and wR2 =15.45% for all

data.

Two zinc atoms are connected to each other by the oxygen atom of a 2 hydroxyl ligand

to form Zn(OH)Zn dimers, and each zinc ion is connected to three [Ta6Cl12(CN)6]3-

clusters by the N end of the CN ligand. Figure 36 shows the coordination environment for

two zinc atoms in a dimer. Figure 37 shows overall framework and the channels. The

channel diameter is roughly 10 Å, which is similar size of [Ta6Cl12(CN)6]3-

building block.

The Ta-Ta bond length is in the range of 2.9100(9) ~ 2.9263(11) Å and the average value

is 2.9152(5)Å. Ta-Cl=2.435(3) ~ 2.448(4)Å, Ta-C=2.214(14) ~ 2.265(14)Å. The average

Ta-C-N angle is 176.7(16)o. The zinc dimer angle connected by oxygen atom is 118.7(9)

o.

The crystal data and structure refinement for compound 6 is shown in Table XXIV.

70

Figure 36. Compound 6 zinc

coordination environment

Figure 37. Crystal structure for compound 6 viewing

along the c axis

71

Table XXIV. Crystal data and structure refinement for compound 6

Empirical formula C3 H0 Cl6 N3 O0.50 Ta3 Zn



Wavelength (Å) Mo (K) 0.71073


Space group C2/c

a (Å) a = 13.222(4)

b (Å) b = 17.081(5)

c (Å) c = 18.051(6)

(°) 90

(°) 94.702(5)

(°) 90

Volume (Å3) 4063(2)

Z 8



) 18.044

F(000) 3152



Index ranges -14<=h<=17, -22<=k<=21,

-23<=l<=23


Independent reflections 4631[R(int) = 0.0568]










*R= (Fo-Fc) / Fo , **wR = {w [(F2

o F2

c)] / w [(F 2

o ) 2]}

0.5

w = [2(F

2o) + (0.0701P)

2+55.6712P]

1 , where P = (F

2o +2 F

2c)/3

72

Table XXV. Selected bond lengths (Å) and bond angles (°) for Compound 6


Ta-C 2.214(14) ~2.265(14) C-Ta-Cl 79.8(5)~ 83.8(5)

Ta-Cl 2.435(3)~ 2.448(4) Cl-Ta-Cl 88.48(14)~ 89.34(14)

Ta- Ta 2.9100(9)~ 2.9263(11) Ta-Cl-Ta 73.20(10)~ 73.59(10)

C≡N 1.094(18)~ 1.16(2) Cl-Ta-Cl 163.19(12)~ 163.26(12)

Zn-O 1.919(10) Ta-Ta-Ta 59.875(18) ~60.31(3)

Zn-N 1.984(16)-1.993(13) Ta-Ta-Ta 89.76(2)~ 90.24(2)

N≡C-Ta 171.7(17)~ 179.3(16)

Zn-O-Zn 118.7(9)

2. Porous metal cluster based coordination polymer

2.1 Zn3[Ta6Cl12(CN)4 X2]2 (X=Cl- or CN

-) (7)

Mixing 10 mL 2 mM of Na3Ta6Cl12(CN)6 in MeOH and 10 mL 3 mM zinc acetate

aqueous solution to stir for 5 minutes, then filter the solution, and leave the filtration

solution in the vial, which is covered by film. Brown plate crystals were obtained after 1

day, as shown in Figure 38. The crystal structure of this compound was determined by

single X-ray single crystal diffraction to correspond to the formula Zn3[Ta6Cl12(CN)4X2]2

(where X is suspected to be Cl or CN).

73

Figure 38. Crystal picture for compound 7 under microscope


Compound 7 crystallizes in the space group Immm, with eight formula units a centered

orthorhombic unit cell. It was not possible to determine whether X is CN or Cl- from

current analysis, therefore, the R values are very big, R1 = 38.28% and wR2 = 63.67%.

Though crystal data was poor quality and could not be refined well, the overall

framework was identified. This compound has a neutral 3D framework containing

[Ta6Cl12(CN)4 X2]3-

and Zn2+

nodes linked to each other by cyanide ligands and/or X

species. Each zinc atom is connected to 4 clusters via two cyanide ligands and/or two CN-

/Cl- ligands. The 3D framework generates channels along the a direction with size of

12x13 Å. As shown in Figure 39. X species is highlighted in pink color.

The Ta-Ta bond length is in the range of 2.911(4) ~ 2.941(3)Å and the average value is

2.9181(6)Å. Ta-Cl=2.438(4) ~2.474(6)Å, Ta-C=2.16(4) ~ 2.284(7)Å, the average Ta-C-

N angle is 172.5(8)o.

74

Figure 39. Crystal structure for compound 7 viewing along the a axis

Two types of zinc geometry are presented here. One is square planar and the other is

tetrahedral. The average Zn-N bond length for the tetrahedral geometry is in the range of

2.14Å. In the square planar geometry zinc environment, average Zn-N≡C bond length is

2.09 Å, and average Zn-X bond length is 2.28 Å. The synergy of these two different zinc

coordination environments enabled the formation of the nanoporous channel in the

compound 7. The crystal data and structure refinement for compound 7 is shown in Table

XXVI.

75

Table XXVI. Crystal data and structure refinement for compound 7

Empirical formula C3 Cl5.50 N2 O Ta3 Zn




Crystal system Orthorhombic

Space group Immm

a (Å) a = 10.754(13)

b (Å) b = 13.342(14)

c (Å) c = 33.60(5)

(°) 90

(°) 9090

(°) 90

Volume (Å3) 4821(11)

Z 8



) 15.149

F(000) 3060



Index ranges -13<=h<=12, -17<=k<=17,

-41<=l<=43





Max. and min. transmission factor 0.1516







*R= (Fo-Fc) / Fo , **wR = {w [(F2

o F2

c)] / w [(F 2

o ) 2]}

0.5

w = [2(F

2o) + (0.2000)

2+ 0.0000P]

1 , where P = (F

2o +2 F

2c)/3

76

Table XXVII. Selected bond lengths (Å) and bond angles (°) for Compound 7


Ta-C 2.16(4) ~2.284(7) C-Ta-Cl 81.40(9)~ 82.6(2)

Ta-Cl 2.438(4) ~2.474(6) Cl-Ta-Cl 87.4(2)~ 89.56(16)

Ta- Ta 2.911(4)~ 2.941(3) Ta-Cl-Ta 73.17(14)~ 73.9(2)

C≡N 1.07(2)~ 1.10(5) Cl-Ta-Cl 163.19(12)~ 163.7(2)

Zn-N 2.10(3)- 2.150(19) Ta-Ta-Ta 59.35(8) ~60.33(4)

Zn-X 2.282(19) Ta-Ta-Ta 89.14(10)~ 90.80(10)

N≡C-Ta 170.7(12)~ 174(3)

The powder pattern for the synthesized compound 7 matches with the simulated powder

pattern, which was calculated from crystal structure, as shown in Figure 41. But after

activating compound 7 under vacuum at 75oC overnight, it lost most of its crystallinity as

indicated by comparing the powder pattern of the activated sample with the original

compound. The color also changed from brown to green, as shown in Figure 40.

The size of the channels and the fact that the 3D framework is neutral led us to carry out

adsorption-desorption study.

Figure 40. Pictures of compound 7 as synthesized and upon activation under vacuum

77

Figure 41. Powder diffraction pattern for compound 7

2.1.2 Infrared spectroscopy

In the starting material Na3Ta6Cl12(CN)6, νCN equals 2133 cm−1

. In compound 7, νCN

shifted left to 2177 cm−1

, which indicates the connectivity to zinc atoms. The IR

spectroscopy is shown in Figure 42, and the assignments for all the major bands in the

spectroscopy are summarized in the Table XXVIII.

Figure 42. Infrared Spectroscopy for compound 7

78

Table XXVIII. IR spectroscopy peaks interpretation for compound 7


)

7 νO-H=3392, νCN=2177, νO-H=1411

2.1.3 Thermogravimetric characterization

Polycrystalline sample of compound 7 was used to study the thermal stability. TGA

shows two distinct weight losses in Figure 43. The first (10%) corresponds to loss of

water and methanol molecules. And the second step (9 %) corresponds to loss of four

cyanide ligands, and two X. The total weight loss is 25%.

Figure 43. TGA measurement for compound 7

79

2.1.4 Host guest interaction study

Compound 7 was activated first under vacuum at 75oC overnight, and color changed from

brown to green, 2mg of this activated product was put in a glass vial with 8mm in

diameter and 3cm in height, then the vial was put into a bigger glass vial with 2cm in

diameter and 6cm in height. Pipette 5mL one of guest molecules from Table XXIX to the

bottom of the bigger vial. All of the guest molecules from Table XXIX were studied.

One week later, the small vial was taken out of the bigger vial, and test samples were

collected to measure powder X-ray diffraction. The observation results are shown in

Table XXIX.

Table XXIX. Properties and color change observation using different guest molecules

* Bp.=boiling point, crys.=crystalline

80

Only anisole lead the recovery of the crystallinity and color back to brown, but the

powder pattern for the anisole accommodated compound 7 showed it is not exactly the

same as the as synthesized compound 7, so it may be another form of crystal type, which

could indicate a crystal to crystal transformation upon anisole adsorption. All the powder

diffraction patterns for different guest molecules diffused into activated compound 7 are

shown in Figure 44.

Figure 44. X-ray powder diffraction for the guest diffusion post-synthesis of compound 7

10 20 30 40

Compound 7 diffuse dimethylaniline

2 theta

Compound 7 calculated

Compound 7 diffuse aniline

Compound 7 diffuse monoethylaniline

10 20 30 40

Compound 7 diffuse anisole

2 theta

Compound 7 calculated

Compound 7 diffuse water

Compound 7 diffuse methanol

Compound 7 diffuse benzene

81

Activation at room temperature results in loss of crystallinity. This experiment indicates

that phenyl ring might be essential to recover the color, while oxygen containing phenyl

rings may be essential to recover the crystallinity. It also indicated that only specific

guests that can fit the framework. In other words, this type of cluster based PCP may

selectively recognize and capture guests in a specific manner.

Infrared spectroscopy showed anisole coordinated with the activated compound 7, as

indicated by the green plot in the Figure 45.

Figure 45. Infrared spectroscopy for anisole diffused compound 7

Table XXX. IR spectroscopy peaks interpretation for compound 7


)

7 with anisole diffusion

νO-H=3435, νCN=2182, νO-H=1411,

νC-O =1495, νC-C= 1239, νO-C= 1036

82

3. Niobium cyanide cluster with dichlorobis(ethylenediamine)nickel(II)

Transition metal complexes provide the possibility to rationally assemble solid-state

coordination networks, because the organic ligands can be used to block some

coordination sites around the transition metal, so the metal complex can direct the

dimension of the assembled framework.

Our group has previously reported on the synthesis of a polymeric hybrid cluster-based

compound with a double layered honeycomb framework55

built of octahedral niobium

cyanochloride clusters and {Zn(en)} metal complexes.

In the previously reported structure each cluster unit connects to six [Zn(en)]2+

groups,

and each [Zn(en)]2+

connects to three cluster units, so the fused six-member rings form

two honeycomb layers, and a common octahedral cluster is shared by two honeycomb

layers. Adjacent layers are stacked on top of each other and interact through weak Van

der Waals interactions only.55

3.1 [Ni(en)2]2[Nb6Cl12(CN)6] • 2.5MeOH (8)

Dichlorobis(ethylenediamine)nickel(II) was synthesized by the following reaction:56

2 [Ni(en)3]Cl2 + NiCl2 → 3 NiCl2(en)2

[Ni(en)2]2[Nb6Cl12(CN)6] • 2.5MeOH was synthesized by adding 16mg (0.01mmol)

of[Me4N]2K2Nb6Cl12(CN)6 in 10mL MeOH to 5.0 mL of 5mg aqueous solution of

NiCl2(en)2 (0.02mmol) under stirring. Purple NiCl2(en)2 aqueous solution changed to

brown upon addition of [Me4N]2K2Nb6Cl12(CN)6, brown-green crystalline materials

83

precipitated after 10 hours. The material was isolated by filtration, washed with two

10mL portions of cold water and two 10mL portions of MeOH, and then dried in air to

obtain 7mg product, yielding 45% based on [Me4N]2K2Nb6Cl12(CN)6. νCN=2111 cm−1

,

2154 cm−1

.


Layering 1 mL of a 2 mM methanolic solution of [Me4N]2K2Nb6Cl12(CN)639

on top of 1

mL 4 mM aqueous solution of NiCl2(en)2 in a 6 mm diameter glass tube led to formation

of brown-green diamond shaped crystals at the boundary of the two solutions after eight

days. (Figure 49).

Figure 46. Crystal picture for compound 8 both under normal light and polarizer

The structure was solved in the space group P-1, with Z = 1. The structural model

incorporated anisotropic thermal parameters for all non-hydrogen atoms except the half

occupied carbon atom and isotropic thermal parameters for all hydrogen atoms. The final

anisotropic full-matrix least-squares refinement gave R1 = 8.06% for observed data and

84

wR2 = 20.07% for all data. A summary of crystal structure refinement data is given in

Table XXXI.

Viewing along the a axis in Figure 50, [Nb6Cl12(CN)6]4-

metal cluster align in the c axis.

Water molecules are in between the layers.. Each cluster is connected to four [Ni(en)2]2+

metal complexes by four CN ligands, and each [Ni(en)2]2+

metal complex is connected to

two [Nb6Cl12(CN)6]4-

metal clusters by the nitrogen ends of CN ligands. The N ends of

the cyanide ligands are located cis to each other.

The Nb-Nb bond length is in the range of 2.9181(11)~2.9298(12)Å and the average value

is 2.9257(5)Å. Nb-Cl=2.449(3)~2.472(2)Å, Nb-C=2.272(10)~2.285(12)Å, the average

Nb-C-N angle is 176.0(10)o.

Figure 47. Crystal structure for compound 8 view along the a axis

85

The purity of the compound 8 as prepared was confirmed by comparing the observed

PXRD to the PXRD calculated from the SCXRD determination. The two PXRD are

shown in Figure 51 and match each other well, but synthesized compound 8 lacks in

crystallinity.

Figure 48. Powder diffraction pattern for compound 8

86

Table XXXI. Crystal data and structure refinement for compound 8

Empirical formula C10 H16 Cl14 N10 Nb6 Ni O2



Wavelength (Å) Cu (K)1.54178

Crystal system Triclinic

Space group P-1

a (Å) a = 8.6017(5)

b (Å) b = 10.6700(5)

c (Å) c = 12.8833(5)

(°) 69.212(3)

(°) 72.010(3)

(°) 87.309(4)

Volume (Å3) 1048.80(9)

Z 1



) 22.285

F(000) 718



Index ranges -9<=h<=9, -12<=k<=12,

-14<=l<=15












*R= (Fo-Fc) / Fo , **wR = {w [(F2

o F2

c)] / w [(F 2

o ) 2]}

0.5

w = [2(F

2o) + (0.1578)

2+ 0.00P]

1 , where P = (F

2o +2 F

2c)/3

87

Table XXXII. Selected bond lengths (Å) and bond angles (°) for Compound 8


Nb-C 2.272(10)~2.285(12) C-Nb-Cl 79.6(3)~ 83.6(3)

Nb-Cl 2.449(3)~2.472(2) Cl-Nb-Cl 87.76(9)~ 90.08(8)

Nb-Nb 2.9181(11)~2.9298(12) N -Cl-Nb 72.57(7)~ 73.37(7)

C≡N 1.122(13)~ 1.158(16) Cl-Nb-Cl 162.55(8)~ 163.16(10)

Ni-N 2.064(10) ~2.128(12) Nb-Nb-Nb 59.74(3) ~60.14(3)

Nb-Nb-Nb 89.77(3)~ 90.23(3)

N≡C-Nb 175.2(10)~ 176.8(11)

N-Ni-N 174.0(5)~ 177.0(4)

3.1.2 Host-guest interaction study

Compound 8 was activated under vacuum at 150oC for three hours. 3mg of this activated

product was put in a glass vial with 8mm in diameter and 3cm in height, and the vial was

put into a bigger glass vial with 2cm in diameter and 6cm in height. Use pipette to add

5mL of iodine to the bottom of the bigger vial, and seal it. Keep the system sealed for one

week. The doping was studied by Infrared spectroscopy and magnetic responsibility.

3.1.3 Infrared spectroscopy

Compound 8 has νCN =2111 cm−1

, 2154 cm−1

as is shown in Figure 52, which indicates

there are two types of cyanide coordination environment, one type is directly connected

with Ni2+

atom, and the other type is stabilized by solvent molecules.

88

After iodine diffusion, one characteristic cyanide vibration peak νCN =2111 cm−1

disappeared, which demonstrate the change in the compound structure, especially cyanide

connection. But since the single crystal after diffusion can’t be obtained, the

corresponding structure couldn’t not be determined.

Table XXXIII. IR spectroscopy peaks interpretation for compound 8 and its doping with

iodine


)

8 νO-H=3351, νC-H=2947, νCN=2154, νCN=2111

Compound 8 with

iodine diffusion

νC-H=3188, νCN==2155 νC-N=1005

Figure 49. Infrared Spectroscopy for compound 8 and its doping with iodine

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3.1.4 Thermogravimetric characterization

TGA measurement shows two distinct weight losses for compound 8 in Figure 54. The

first (5.0%) corresponds to loss of all coordinated and free solvent molecules at

temperature below 100oC. The compound continues to lose weight after 200

oC until

400oC, which stage corresponds to 25% weight lost, including 10% cyanide and 15%

ethylenediamine. The compound will continue decompose after 400oC.

Figure 50. Thermogravimetric analysis for compound 8

90

CONCLUSION

The research presented in this thesis is primarily concerned with understanding the

principles to use metal cluster as building blocks in supramolecular assembly to

synthesize coordination polymers, and applying experimental control to get desired

structures and properties of these new hybrid materials. Metal cluster contained

coordination polymers demonstrate to have versatile and intriguing structures, and are

showing promising application in the area of catalysis, magnetism and adsorption.

The research objective was to prepare novel coordination polymers using metal cluster as

nanosize building blocks, and characterize them in structures and properties. The

coordination polymers we studied contain three types of system:

i) Direct self-assembly of octahedral tantalum clusters [Ta6Cl12(CN)6]3-

and rare

earth element. Two types of topologies can be obtained from single crystal

analysis. The diversity on the resulting structure from two chemical components

can be rationalized to be size effect, angularity and distortion of the molecular

building blocks.

ii) Under various conditions, self-assembly of rare earth metal Eu3+

, octahedral

building blocks [Ta6Cl12(CN)6]3-

, facilitated by the rigid co-ligand dpdo (dpdo =

4,4'-dipyridyl N,N'-dioxide, C10H8N2O2) to generate three types of frameworks.

iii) Self-assembly of metal clusters with transition metals or metal complexes, two

types of metal cluster containing coordination polymers were synthesized.

Overall, the main effort of this work is devoted to understanding the basic principles in

supramolecular assembly using metal cluster, and explore their specific properties.

91

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SCHOLASTIC VITA

LEI CHEN

Birthdate: June 16, 1985

Birthplace: Qian’an, China

Education Background

Beijing University of Chemical Technology (BUCT)-Beijing, P. R. China

September 2003-June 2007- Bachelor of Science in Materials Science

Wake Forest University (WFU)-Winston Salem, NC, USA

January 2009-August 2011- Master of Science in Materials Chemistry

Professional Experience

Targacept Inc. -Winston Salem, NC, USA

May-August 2011- Summer Internship

Wake Forest University(WFU)-Winston Salem, NC, USA

January 2009-May 2011- Teaching Assistant

Procter& Gamble- Beijing, P.R. China

September 2007-December 2008- Product Design Researcher

Awards

International Research Fellowship, ICMR, 2010

Graduate Richter Fellowship Award, WFU, 2010

94

Presentations

L. Chen, J. J. Zhang, C. S. Day, A. Lachgar: Europium containing cationic layered 2D

frameworks templated by the paramagnetic [Ta6Cl12(CN)6]3-

octahedral metal clusters.

Presented at Annual Sigma Xi meeting. Raleigh, NC, USA. November 2010.

L. Chen, J. J. Zhang, C. S. Day, A. Lachgar: Octahedral Metal Clusters as Templates of

Rare Earth Metal Coordination Polymers. Presented at the ACS Southeastern Regional

Meeting. San Juan, Puerto Rico. October 2009.

Professional Societies

2010- present, Materials Research Society

octahedral metal clusters as molecular building … · of coordination polymers: synthesis,...

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